# Porting



## somebigman (Sep 12, 2022)

Have a new Stihl 661-c and would like to have it ported. Live in Indiana and would prefer someone in the midwest to do the work. Thanks in advance for the reply.


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## link (Sep 12, 2022)

You gonna use the saw for showing cutting cookies at you tube - or milling?
If you are gonna use it for milling that saw is perfect just as it is, you don't want to degrade it's torque by having someone going wild with a grinding tool raising the exhaust timing on it. And brake the nikasil coating between the cylinder and the port bevel, that sure aint gonna make it last longer.

Performance blow away at the local GTG with a full engine rebuild after every run - is quite the opposite of milling.
You gonna run that saw at full tit for long hours each time, it better be up for it - endurance and torque.
Your saw was made for it - just as it is.


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## somebigman (Sep 13, 2022)

Good to know. Thank You.


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## ElevatorGuy (Sep 13, 2022)

@huskihl is in Michigan.


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## huskihl (Sep 13, 2022)

I’m in Michigan, but there’s a pretty long waiting list. If January or February works for you, send me a PM


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## huskihl (Sep 13, 2022)

Thank you, @ElevatorGuy


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## huskihl (Sep 13, 2022)

link said:


> You gonna use the saw for showing cutting cookies at you tube - or milling?
> If you are gonna use it for milling that saw is perfect just as it is, you don't want to degrade it's torque by having someone going wild with a grinding tool raising the exhaust timing on it. And brake the nikasil coating between the cylinder and the port bevel, that sure aint gonna make it last longer.
> 
> Performance blow away at the local GTG with a full engine rebuild after every run - is quite the opposite of milling.
> ...


I only build work saws, but I test my power gains by cutting cookies. If I were to only cut firewood while testing, I’d need 30 pulp cord of logs every year. I’m not in the business of splitting and selling firewood though. 

There are many builders out there that build race saws and GTG type saws only, but you’re painting with a broad brush by fitting me in with “cookie cutters”. My goal is to make a saw cut faster using the same size bar as before, or to be able to run a longer bar than what was possible before.


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## TRTermite (Sep 13, 2022)

huskihl said:


> I only build work saws, but I test my power gains by cutting cookies. If I were to only cut firewood while testing, I’d need 30 pulp cord of logs every year. I’m not in the business of splitting and selling firewood though.
> 
> There are many builders out there that build race saws and GTG type saws only, but you’re painting with a broad brush by fitting me in with “cookie cutters”. My goal is to make a saw cut faster using the same size bar as before, or to be able to run a longer bar than what was possible before.


Your COMMENT reminds me of an old saying. "You Kicked the CAT out of that DOG FIGHT"


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## huskihl (Sep 13, 2022)

TRTermite said:


> Your COMMENT reminds me of an old saying. "You Kicked the CAT out of that DOG FIGHT"


Some guys give ported chainsaws a bad rap, as some builders do things a little bit differently and have their own opinion, right or wrong, about what makes a good work saw. Maybe they ran a ported saw and it didn’t last and the builder wouldn’t fix it or they ran one and they felt it wasn’t worth the cost. They get soured on the idea and due to that one bad experience, they don’t feel it’s a worthy venture. To each their own, I guess. I just wish they’d educate themselves before saying that all ported saws won’t last or that they can’t perform a specific function better


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## TRTermite (Sep 13, 2022)

huskihl said:


> Some guys give ported chainsaws a bad rap, as some builders do things a little bit differently and have their own opinion, right or wrong, about what makes a good work saw. Maybe they ran a ported saw and it didn’t last and the builder wouldn’t fix it or they ran one and they felt it wasn’t worth the cost. They get soured on the idea and due to that one bad experience, they don’t feel it’s a worthy venture. To each their own, I guess. I just wish they’d educate themselves before saying that all ported saws won’t last or that they can’t perform a specific function better


My DAD was a firm believer in "Because I said so" Most of the time it wasn't. You have a polite way of pointing out differences of opinions.


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## Lightning Performance (Sep 13, 2022)

huskihl said:


> Some guys give ported chainsaws a bad rap, as some builders do things a little bit differently and have their own opinion, right or wrong, about what makes a good work saw. Maybe they ran a ported saw and it didn’t last and the builder wouldn’t fix it or they ran one and they felt it wasn’t worth the cost. They get soured on the idea and due to that one bad experience, they don’t feel it’s a worthy venture. To each their own, I guess. I just wish they’d educate themselves before saying that all ported saws won’t last or that they can’t perform a specific function better


Well said Kevin.

Some people don't bevel ports, chamfer bolts holes or even bother looking at the rest of the tool. I build my saws specifically for milling now and you and I both know that has nothing to do with how long something will last or it's wear properties progress on parts. The guy who says porting is bad hasn't a clue what is really involved. Sure we could just be lumped in with others but that really should piss off everyone who does do nice work. I know for fact you/I can make the rings last longer that stock. Maybe the guy doesn't understand the time that goes into all those correct shapes, bevels in the right place when needed and dare I say just clean out the port runners?... oh my maybe I've said too much. 

Not fixing stock related issues like black transfer ports and choking exhaust with leass not more port intake volume really must make your tools last longer, sure. Ima go over here, be quiet and stick my head in ****ing sand.

Bye now... ported heads suck.... wtf kind of comet is that


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## Lightning Performance (Sep 13, 2022)

somebigman said:


> Good to know. Thank You.


Ignore the post above this posted by Link.


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## somebigman (Sep 14, 2022)

link said:


> You gonna use the saw for showing cutting cookies at you tube - or milling?
> If you are gonna use it for milling that saw is perfect just as it is, you don't want to degrade it's torque by having someone going wild with a grinding tool raising the exhaust timing on it. And brake the nikasil coating between the cylinder and the port bevel, that sure aint gonna make it last longer.
> 
> Performance blow away at the local GTG with a full engine rebuild after every run - is quite the opposite of milling.
> ...


 Not going to use the saw for "cookie cutting", mostly for milling. I have some 24" diameter walnut and cherry I plan to mill. I think I will leave the Saw stock.


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## somebigman (Sep 14, 2022)

TRTermite said:


> Your COMMENT reminds me of an old saying. "You Kicked the CAT out of that DOG FIGHT"


Never heard that one before, don't even know what it means.


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## TRTermite (Sep 14, 2022)

somebigman said:


> Never heard that one before, don't even know what it means.


When some "person" is Stirring the pot also known as trolling, one of the old cliches was "Throwing a Cat in a DOG FIGHT". This comment Merely tweaks that cliché to say that some one removed the "Thrown in cat" so the Dogs can return to "Business as usual" without the distraction of said cat.. To say "KICK the Cat" suggests that anyone would be close to insane to try and "GRAB" a cat out of a dog fight. It is an expression and no animals were harmed or intended harm with my comment.


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## Stihl 041S (Sep 14, 2022)

link said:


> You gonna use the saw for showing cutting cookies at you tube - or milling?
> If you are gonna use it for milling that saw is perfect just as it is, you don't want to degrade it's torque by having someone going wild with a grinding tool raising the exhaust timing on it. And brake the nikasil coating between the cylinder and the port bevel, that sure aint gonna make it last longer.
> 
> Performance blow away at the local GTG with a full engine rebuild after every run - is quite the opposite of milling.
> ...


Only cookie cutting done with my MM 090 is at GTGs. Folks want to play with one and there is usually a 4-5 foot log to try it
I have ported saws from 22 to 135cc. Use them hard.
They make cutting cords and cords of hardwood much easier.
On me AND the saw.

Thanks saw saw is NOT perfect as is.

Much more torque ………why wouldn’t you port a saw?


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## link (Sep 15, 2022)

somebigman said:


> Not going to use the saw for "cookie cutting", mostly for milling. I have some 24" diameter walnut and cherry I plan to mill. I think I will leave the Saw stock.


Well you certainly have the absolute perfect saw for that particular job.

Note the cut surface when he's done... he knows what he's doing.


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## link (Sep 15, 2022)

Stihl 041S said:


> Much more torque ………why wouldn’t you port a saw?


Is that so, really ? So the exhaust opening was lowered or what


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## Lightning Performance (Sep 15, 2022)

link said:


> Is that so, really ? So the exhaust opening was lowered or what


That statement proves you don't understand time area but please go on.


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## link (Sep 15, 2022)

Lightning Performance said:


> That statement proves you don't understand time area but please go on.


Well, I am slightly more than mediocre interested in engines and I do understand endurance and factory warranty.


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## link (Sep 15, 2022)

That's a kill yes ?


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## maulhead (Sep 15, 2022)

huskihl said:


> I only build work saws, but I test my power gains by cutting cookies. If I were to only cut firewood while testing, I’d need 30 pulp cord of logs every year. I’m not in the business of splitting and selling firewood though.
> 
> There are many builders out there that build race saws and GTG type saws only, but you’re painting with a broad brush by fitting me in with “cookie cutters”. My goal is to make a saw cut faster using the same size bar as before, or to be able to run a longer bar than what was possible before.



All I will say it some saws are pitiful stock, and really come alive once ported. 

461 for example, choked up tiny exhaust hole, limited coil, etc, I was not impressed with one in stock form at all. 

Ported a 461 is a completely different saw. Once I ran a ported 461, using a stock one was almost painful.


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## link (Sep 15, 2022)

maulhead said:


> All I will say it some saws are pitiful stock, and really come alive once ported.
> 
> 461 for example, choked up tiny exhaust hole, limited coil, etc, I was not impressed with one in stock form at all.
> 
> Ported a 461 is a completely different saw. Once I ran a ported 461, using a stock one was almost painful.


one thing I find funny about that is that you amateurs does such a better job tuning a saw than what educated knowledge does. It must be nothing less than a miracle, or not true.


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## maulhead (Sep 15, 2022)

Must be true....


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## link (Sep 15, 2022)

That's over the top buddy...


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## maulhead (Sep 15, 2022)

link said:


> That's over the top buddy...




No worse then your statement in your other poast.


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## link (Sep 15, 2022)

maulhead said:


> No worse then your statement in your other poast.


Ok.


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## link (Sep 15, 2022)

maulhead said:


> No worse then your statement in your other poast.


Exactly what does it say that you react negatively on to ? 
That's not a trick question, I'm just asking...


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## link (Sep 15, 2022)

I'm right here - wide open to any attack.... 
I'm not a fool though.


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## Lightning Performance (Sep 15, 2022)

link said:


> Well, I am slightly more than mediocre interested in engines and I do understand endurance and factory warranty.


Factory warranties, ok.
Thanks it's all clear as mud now.


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## Lightning Performance (Sep 15, 2022)

maulhead said:


> Must be true....
> 
> View attachment 1017361


Pencil me in I need all the miracles I can get, beg borrow, ect...


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## Lightning Performance (Sep 15, 2022)

link said:


> I'm right here - wide open to any attack....
> I'm not a fool though.


Attack?...
We're just looking for information. We need to know what is what so give us the update, hidden knowledge or at least some clue.
Help a guy out.
Please


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## Lightning Performance (Sep 15, 2022)

Just my two cents.
My holes are all big but with good flow. 
Bigger is better right?... I mean who wants a tiny exit port, yes?
I'll ketchup eventually


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## link (Sep 15, 2022)

My two cents would be that a stock MS661c - is a pretty awesome machinery... why change a proven winning team ?


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## link (Sep 15, 2022)

Exactly why would you do that, better have a good reason to wreck the Stihl recommendation or what yes ?


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## link (Sep 15, 2022)

And I mght be a nobody to the FSB or the IRA, but to the world I'm a king.
Because i SAY i AM. 
You think I'm no better than yourself you are perfectly right though...


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## huskihl (Sep 15, 2022)

link said:


> Is that so, really ? So the exhaust opening was lowered or what


That’s exactly what happens in most of my ported saws


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## olyman (Sep 15, 2022)

link said:


> And I mght be a nobody to the FSB or the IRA, but to the world I'm a king.
> Because i SAY i AM.
> You think I'm no better than yourself you are perfectly right though...


ahahhahhhahhahahaahhaaaaaaa,, what a crock of BS


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## StihlPotlicker (Sep 16, 2022)

somebigman said:


> Have a new Stihl 661-c and would like to have it ported. Live in Indiana and would prefer someone in the midwest to do the work. Thanks in advance for the reply.


I put a Max Air flow filters and a Egan straight shot on my 661C that i used on my Logosol chainsaw mill, before i bought a G660 to see how long it would last as a Chainsaw mill lol.


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## Stihl 041S (Sep 16, 2022)

huskihl said:


> That’s exactly what happens in most of my ported saws


Thank you. That probably won’t be answered. 
That was my post he quoted. 
He seems young and childish ……..a youthful knowledge……..

Probably never ran a ported saw. Or been to a GTG. 
Typical of a good Porter looks like this


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## TheLaundryMan (Sep 17, 2022)

Hey so how much does it cost to get my 661 ported? You got me thinking I need to let her breathe better!


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## Stihl 041S (Sep 17, 2022)

Usually around $300 plus shipping 
Someone correct me if I’m off.


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## TRTermite (Sep 17, 2022)

Stihl 041S said:


> Usually around $300 plus shipping
> Someone correct me if I’m off.


I have heard some that prices have went up a "Tad"


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## TheLaundryMan (Sep 17, 2022)

Inflation been rough on everyone.


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## Stihl 041S (Sep 17, 2022)

TRTermite said:


> I have heard some that prices have went up a "Tad"


Yeah. It’s been a couple of years since I read it here. 
Thanks


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## link (Sep 17, 2022)

Well if you get past my critical comments you know what you're doing at least, thats my aim - not criticism.
At the sales marked I would never consider a templed with saw, because I don't know exactly whats done with it.
A perfectly stock Stihl or Husky 92cc, thats clean sheets and something might worth investing in.
Anyway whenever I see this I cant help thinking to my self; a 661 + 300 dollas - perhaps you bought the wrong saw in the first place...


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## Stihl 041S (Sep 17, 2022)

link said:


> Well if you get past my critical comments you know what you're doing at least, thats my aim - not criticism.
> At the sales marked I would never consider a templed with saw, because I don't know exactly whats done with it.
> A perfectly stock Stihl or Husky 92cc, thats clean sheets and something might worth investing in.
> Anyway whenever I see this I cant help thinking to my self; a 661 + 300 dollas - perhaps you bought the wrong saw in the first place...


It would be the 881……much heavier and a lot more $$$
And your bars don’t fit. 
Where as a port job gaining 35-40% in HP ………you have gone up a class
A port job usually means stepping up a class in power
A 60cc doing the job of a 70cc easily with less weight. 
And ported saws run cooler and last just as long or longer
Just saying what I’ve seen happen


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## link (Sep 17, 2022)

Stihl 041S said:


> Where as a port job gaining 35-40% in HP …


So, a MS661 is at about 5,4kw / 7,25hp, you saying that he will get 7,5kw / 10hp from that saw without compromising torque or sustainability?
I simply don't think that will be true, sir.


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## Stihl 041S (Sep 17, 2022)

Back a few posts I posted a dyno result……can’t hold that curve without torque
And I’ve flogged a ported 026 for 6 years till I got a ported 261
The 026 still runs fine. 
As a friend said “That saw chits wood!!”


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## huskihl (Sep 17, 2022)

link said:


> So, a MS661 is at about 5,4kw / 7,25hp, you saying that he will get 7,5kw / 10hp from that saw without compromising torque or sustainability?
> I simply don't think that will be true, sir.


10.5 to 11hp, actually


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## link (Sep 20, 2022)

huskihl said:


> 10.5 to 11hp, actually


Alright, I trust you...... good luck with that.


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## huskihl (Sep 20, 2022)

link said:


> Alright, I trust you...... good luck with that.


There are dyno sheets of before and after. Some saws only gain 15-20% while others end up with 40-45% more hp. A woods ported 65cc saw can be up over 8.5 HP. My 661 is 10.5 HP and I know of others that are over 11.


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## Stihl 041S (Sep 20, 2022)

huskihl said:


> There are dyno sheets of before and after. Some saws only gain 15-20% while others end up with 40-45% more hp. A woods ported 65cc saw can be up over 8.5 HP. My 661 is 10.5 HP and I know of others that are over 11.


Some of the good echos REALLY wake up.


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## link (Sep 20, 2022)

Yea, its just that HP is directly related to rpm and torque is directly related to stroke and cc...
That will in fact reduce the life of your engine, but it might be fun while it lasts - just like my tobacco smoking.
It will be great fun for a short time. Had my xray scan of my lungs today - how fun is that really?
For cutting cookies at the you tube - by all means. But for milling - thats all a about the opposite.


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## Leeroy (Sep 20, 2022)

link said:


> Yea, its just that HP is directly related to rpm and torque is directly related to stroke and cc...
> That will in fact reduce the life of your engine, but it might be fun while it lasts - just like my tobacco smoking.
> It will be great fun for a short time. Had my xray scan of my lungs today - how fun is that really?
> For cutting cookies at the you tube - by all means. But for milling - thats all a about the opposite.


Tried to pm you link. Hope the scan today went well.


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## huskihl (Sep 20, 2022)

Stihl 041S said:


> Some of the good echos REALLY wake up.


Most definitely


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## huskihl (Sep 20, 2022)

link said:


> Yea, its just that HP is directly related to rpm and torque is directly related to stroke and cc...
> That will in fact reduce the life of your engine, but it might be fun while it lasts - just like my tobacco smoking.
> It will be great fun for a short time. Had my xray scan of my lungs today - how fun is that really?
> For cutting cookies at the you tube - by all means. But for milling - thats all a about the opposite.


Saws can be ported for milling as well. Milling saws would be ported differently than cookie cutters, obviously. 

You clearly don’t own a properly ported saw, the way you’re carrying on. But that’s no reason to go about the path you’re taking in saying that ported saws won’t last and are only good for play.


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## link (Sep 20, 2022)

Well, if the best and most payed scientists in the world came up with a chainsaw engine based on all the parameters we know - made it like that, why would they make it so bad compared to what you rednecks can achieve with a bottle of gin?


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## huskihl (Sep 20, 2022)

link said:


> Well, if the best and most payed scientists in the world came up with a chainsaw engine based on all the parameters we know - made it like that, why would they make it so bad compared to what you rednecks can achieve with a bottle of gin?


Classic. 
I will continue to sit in my garage working on saws drinking my coffee while you are busy ****ing off


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## link (Sep 20, 2022)

huskihl said:


> Classic.
> I will continue to sit in my garage working on saws drinking my coffee while you are busy ****ing off


Im just saying; Husqvarna and Sthil have the best educated and most payed engine engineers hired in the world, and you just said that you just know so much better? Id say thats not really a wise attitude to the matter.


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## link (Sep 20, 2022)

You know.. perhaps some really important detail just slipped your mind...


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## huskihl (Sep 20, 2022)

link said:


> You know.. perhaps some really important detail just slipped you mind...


I’m sure several important details have slipped my mind over the years. It happens. 

But the major manufacturers are limited by EPA constraints. A single pencil sized hole in the muffler outlet designed to keep the heat inside of the can to burn off excess hydrocarbons in an 80cc saw comes to mind. 

You’ve not proven that a stock saw will outlast a ported one, let alone the opposite.


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## link (Sep 20, 2022)

huskihl said:


> I’m sure several important details have slipped my mind over the years. It happens.
> 
> But the major manufacturers are limited by EPA constraints. A single pencil sized hole in the muffler outlet designed to keep the heat inside of the can to burn off excess hydrocarbons in an 80cc saw comes to mind.
> 
> You’ve not proven that a stock saw will outlast a ported one, let alone the opposite.


But there's a pretty vicious billion dollars competition out there... to have the most powerful chainsaw to weight.
That's not the knowledge of "you", thats the knowledge of a "team" of top educated engineers...

You just saying they are all wrong... and that "you" are right.
Just how many people does that - 5 billion ?


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## StihlPotlicker (Sep 20, 2022)

Stihl 041S said:


> Usually around $300 plus shipping
> Someone correct me if I’m off.


$350.00 last I paid for Tree Monkey to port my 881


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## StihlPotlicker (Sep 20, 2022)

link said:


> But there's a pretty vicious billion dollars competition out there... to have the most powerful chainsaw to weight.
> That's not the knowledge of "you", thats the knowledge of a "team" of top educated engineers...
> 
> You just saying they are all wrong... and that "you" are right.
> Just how many people does that - 5 billion ?


my buddy out in Cali, was cutting on the fire units and had a 500i ported and max air flow put on. and did a YouTube video and he had Stihl headquarters wanting to know where he bought the saw and who did the port work on it. I guess they didn't take to kindly to the 500i being bashed LOL. and they did a ton of field testing on the 500i before they released it too.


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## Lightning Performance (Sep 20, 2022)

huskihl said:


> Classic.
> I will continue to sit in my garage working on saws drinking my coffee while you are busy ****ing off


Damn coffee drinkers


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## Lightning Performance (Sep 20, 2022)

StihlPotlicker said:


> my buddy out in Cali, was cutting on the fire units and had a 500i ported and max air flow put on. and did a YouTube video and he had Stihl headquarters wanting to know where he bought the saw and who did the port work on it. I guess they didn't take to kindly to the 500i being bashed LOL. and they did a ton of field testing on the 500i before they released it too.


Is the new bashed the 500I thread?
Just asking.

Ported stuff sucks man


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## Stihl 041S (Sep 20, 2022)

link said:


> Im just saying; Husqvarna and Sthil have the best educated and most payed engine engineers hired in the world, and you just said that you just know so much better? Id say thats not really a wise attitude to the mat


You think the best engine builders are factory????
Cosworth went against the WORLD as a privateer
And beat everyone……
Huski and stihl May have the most educated and highest paid. And that don’t mean squat……
They just aren’t the best.

And what experience do you have with well ported saws?
Oh……..none……


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## Sierra_rider (Sep 20, 2022)

link said:


> But there's a pretty vicious billion dollars competition out there... to have the most powerful chainsaw to weight.
> That's not the knowledge of "you", thats the knowledge of a "team" of top educated engineers...
> 
> You just saying they are all wrong... and that "you" are right.
> Just how many people does that - 5 billion ?


It's already been said, but stock saws are limited by sound and emissions regulations. Power isn't their only consideration, they also have to have a quiet saw and one that runs cleanly. It seems pretty reasonable that, if you don't care about sound or emissions, you can build a saw that's optimized for power.

I'm not a guy that's a professional porter, just merely an informed "redneck," although I mostly drink hipster IPA beers or whiskey instead of gin. Just because I'm not a Stihl engineer, doesn't mean that I'm just some idiot with a dremel...I'm actually an idiot with flex shaft grinders and a lathe.

Even some idiot hillbilly like me has an understanding of how compression, port timing, and even port shapes affect the powerband of the saw. Coupled with exhaust mods, I can build a saw that is a definite improvement over stock. All of my saws are work saws...they are used for falling trees or are climbing saws. I'm usually not reinventing the wheel with them, just prioritizing power over noise and EPA compliance. 

I'll add that that I don't hold saw engineers on some pedestal...like we already established, they are designed as a compromise for factors that a lot of the end users don't care about. Besides that, saw technology is in the dark ages compared to other types of 2 stroke motors. Just look at dirtbikes...they've had powervalves and reed valves for the better part of 40 years now. Going even further, most of them are now case-reed inducted with boost ports located where the intake port would be on a cylinder fed jug. Just looking at how much the transfers can flow compared to a traditional 2 stroke motor is eye opening. Suddenly, saw motors don't look so high tech. I understand that they have to build the saw in a small, lightweight package, but it's not the dark art you think it is.


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## CJ1 (Sep 21, 2022)

link said:


> But there's a pretty vicious billion dollars competition out there... to have the most powerful chainsaw to weight.
> That's not the knowledge of "you", thats the knowledge of a "team" of top educated engineers...
> 
> You just saying they are all wrong... and that "you" are right.
> Just how many people does that - 5 billion ?


Hummmm, let me think, what is the difference between the highly edumacated enganneer and the home saw builder? Budget. You think that the OEM's are going to spend the time and $$ that Kevin and other saw porters do to make things "just right" NO. They just care about profit because of the Bean counters. AND the saws have to last with idiots that sometime get them into their hands. So there is the difference. I have only scattered 1 modded saw and that was because of the piston being lightened and windowed too much. The rest have been running great, some for years so far. My 346 has roughly 75+ gallons of gas through it with my 562 closely following that. Both get ran HARD. Kevin's saws perform as he states and usually better. CJ


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## SCHallenger (Sep 21, 2022)

link said:


> Im just saying; Husqvarna and Sthil have the best educated and most payed engine engineers hired in the world, and you just said that you just know so much better? Id say thats not really a wise attitude to the matter.


I'm pretty sure the engineers you mention have some restrictions on what they are paid to design. It would be very interesting to know if any of them run saws of their own design & whether or not any of them have been "tweaked" a bit to enhance performance.


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## Stihl 041S (Sep 21, 2022)

SCHallenger said:


> I'm pretty sure the engineers you mention have some restrictions on what they are paid to design. It would be very interesting to know if any of them run saws of their own design & whether or not any of them have been "tweaked" a bit to enhance performance.


Very true 
A friend of mines dad worked at ford engine R&D. 
They put Chevy heads on a 289. 
Project over it went out the back door. As many concept cars did also. 

It would push a 20’ jet boat. Big Block area for sure. 

But they never sold that version. Lol


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## SCHallenger (Sep 21, 2022)

Stihl 041S said:


> Very true
> A friend of mines dad worked at ford engine R&D.
> They put Chevy heads on a 289.
> Project over it went out the back door. As many concept cars did also.
> ...


Yeah, I get it. At one time I had a 1973 Olds Toronado with a 455 powerplant which had some early version a PCvalve & some recycling technology. This was known to rob the engine of some power. I knew a guy who put this stuff on by day & took it off by night! I had him "unrecycle" my Toro, & it really perked it up as well as improving fuel economy!! There is no doubt that the engine having been relieved of it's EPA (employment prevention agency) mandated burden would not be subjected to as much wear & tear & would have a much longer life span!


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## Stihl 041S (Sep 21, 2022)

SCHallenger said:


> Yeah, I get it. At one time I had a 1973 Olds Toronado with a 455 powerplant which had some early version a PCvalve & some recycling technology. This was known to rob the engine of some power. I knew a guy who put this stuff on by day & took it off by night! I had him "unrecycle" my Toro, & it really perked it up as well as improving fuel economy!! There is no doubt that the engine having been relieved of it's EPA (employment prevention agency) mandated burden would not be subjected to as much wear & tear & would have a much longer life span!


Had a one ton 4X4 Chevrolet van. Part of a bunch made for the phone company

Tuned it on the Dyno after all smog stuff was removed.
Passed.California smog test


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## North by Northwest (Sep 22, 2022)

All production engines are designed to serve a finite period of time . The old extended serviceability of early Chev 283 or Ford 289 & Dodge 318 will not be replicated . Durability & simplicity of repair are today not a part of the master plan . Today production engines like much of every thing produced , is disposable commodities . That must meet even more epa restrictive regulations & work within those defined perimeters for a specific hour life . So as I said before , a good engine builder can fine tune & massage these set points for a better overall performance package & potential longer life cycle . How much is determined by how far he goes . e.g. Simple minor porting & polishing & muffler modification or more radical piston & ring porting & muffler redesign or replacement . Yes people like Kevin & Randy & others have yrs of experience within these design changes that can provide a durable & more reliable daily cutter , to a all out performance saw on the ragged edge !


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## North by Northwest (Sep 22, 2022)

Stihl 041S said:


> Had a one ton 4X4 Chevrolet van. Part of a bunch made for the phone company
> 
> Tuned it on the Dyno after all smog stuff was removed.
> Passed.California smog test


A well tuned & carburated engine tuned on the lean side within fuel and timing numbers will easily pass even todays restrictive epa regulations in most cases . However must maintain those numbers consistently & continually . This requires constant preventative maintenance , which requires constant tweaking that the average owner does not maintain adequately unfortunately !


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## Lightning Performance (Sep 22, 2022)

Sierra_rider said:


> It's already been said, but stock saws are limited by sound and emissions regulations. Power isn't their only consideration, they also have to have a quiet saw and one that runs cleanly. It seems pretty reasonable that, if you don't care about sound or emissions, you can build a saw that's optimized for power.
> 
> I'm not a guy that's a professional porter, just merely an informed "redneck," although I mostly drink hipster IPA beers or whiskey instead of gin. Just because I'm not a Stihl engineer, doesn't mean that I'm just some idiot with a dremel...I'm actually an idiot with flex shaft grinders and a lathe.
> 
> ...


Wait now... I thought us fools with grinders and such were in the dark ages, hum.
A chainsaw won't benefit much from exhaust valves imho. Other valves, maybe.

Casting a proper cylinder and updating ancient technology would be and improvement on these old vibration boxes we still use. Engineering usually nails it till they actually try to get it built. Then comes the long walk down to their fabrication shop for some more learning about things like straight ports won't fit or don't work well for X application. And the ever popular,
"We have no way to service that design."  from your builders.
Soon after a lawyer chimes in and says, "Nope... we can't insure that either, sorry." 
Then the EPA or DEP maybe CARB, just take your pic shuts it down after fifty hours testing


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## link (Sep 23, 2022)

Well, no doubt professional porting can achieve something when you discard environmental considerations.
But you see what you want to see... and you hear what you want to hear...
and increasing rpm and hp will certainly reduce endurance - just how it is. So how you gonna sell it - barely used 



Burning your candle in both ends at the same time does - what ?


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## link (Sep 23, 2022)

Down at the chainsaw forum bucking fire wood you might have fun, but in "this" part of the forum - you are looking for love at "all" the wrong places.


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## Sierra_rider (Sep 23, 2022)

link said:


> Well, no doubt professional porting can achieve something when you discard environmental considerations.
> But you see what you want to see... and you hear what you want to hear...
> and increasing rpm and hp will certainly reduce endurance - just how it is. So how you gonna sell it - barely used
> View attachment 1019350
> ...



...but higher rpm means less time actually cutting, so is it not a wash? I'd also venture to guess that less energy is wasted as heat...


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## link (Sep 23, 2022)

Sierra_rider said:


> ...but higher rpm means less time actually cutting, so is it not a wash? I'd also venture to guess that less energy is wasted as heat...


Yeah, you see what you wanna to see and you hear what you want to hear...


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## huskihl (Sep 23, 2022)

link said:


> Yeah, you see what you wanna to see and you hear what you want to hear...


Same as you, no?


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## Stihl 041S (Sep 23, 2022)

North by Northwest said:


> A well tuned & carburated engine tuned on the lean side within fuel and timing numbers will easily pass even todays restrictive epa regulations in most cases . However must maintain those numbers consistently & continually . This requires constant preventative maintenance , which requires constant tweaking that the average owner does not maintain adequately unfortunately !


Never spent too much time around average people.
Most friends did serious builds.
Some worked for Gurney
A couple were salt flat folks
One built 9 cars from scratch……..
One father&son raced their home built dragster from LA to Indy to win their class
Home built as to casting their own intake manifolds
9.00 quarters……..never did 8.99……so close.
That 350 in. The 4x4 went 250k miles.
I was lucky to be with those folks


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## Stihl 041S (Sep 23, 2022)

link said:


> Yeah, you see what you wanna to see and you hear what you want to hear...


How much experience have you had with saws?
Much less ported ones?


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## Stihl 041S (Sep 23, 2022)

link said:


> Down at the chainsaw forum bucking fire wood you might have fun, but in "this" part of the forum - you are looking for love at "all" the wrong places.


Since you are taking that track…….why do folks that mill a lot have them ported for milling……actually milling………not just talking.


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## link (Sep 28, 2022)

Stihl 041S said:


> Since you are taking that track…….why do folks that mill a lot have them ported for milling……actually milling………not just talking.


Because they just wants to do it quicker, and don't really care about the long term cost.
The significance of "quicker" might not be all that much though, as everything - it's the operator that matters. 
For milling I would want sustainability and solid reliable - that's what you pay Stihl for doing.


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## biggerstaff94 (Sep 28, 2022)




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## link (Sep 28, 2022)

Better get the live image, it kinda sets the standard... thanks buddy.


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## HumBurner (Sep 29, 2022)

link said:


> Im just saying; Husqvarna and Sthil have the best educated and most payed engine engineers hired in the world, and you just said that you just know so much better? Id say thats not really a wise attitude to the matter.



I'd wager a ported saw that either Boeing, Lockheed-Martin, or Dow/Monsanto have the highest paid engineers, not Stihl or Husqy



link said:


> Well, if the best and most payed scientists in the world came up with a chainsaw engine based on all the parameters we know - made it like that, why would they make it so bad compared to what you rednecks can achieve with a bottle of gin?



Because emissions and operators that don't maintain their equipment properly.


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## Stihl 041S (Sep 29, 2022)

And as to engine engineers……..stihl has to make a vanilla flavored engine. 
Not stressed in any way really. 

Formula one…….$50,000 pistons……each. 

The motors to test the transmission……14” in diameter and 20 inches long. To fit the envelope. 
Idles at 4500 rpm and hits 22,000 in 1/50th of a second. 
960 HP
Now tell me about the best educated engine engineer in the world. 
And like the last poster mentioned…….aerospace engineers are t too shabby. 
Pump 15 tons of fuel per second at 1350 psi…….or fuel a small 2 stroke. 
Which takes more finesse……..and education.


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## scut207 (Sep 29, 2022)

If the engine is inefficient at getting the heat out, its heat retained. Theres no such thing as perfection in this from some dude with a slide rule... Theres as good as you can get in the operating environment, any improvement is an improvement. Excess heat is the enemy of longevity.

Even as ignorant as I likely am to porting and 2 cycle theory:

Engineers at the big companies aren't looking at the design at the level of every single saw produced. They are looking at the tolerances that their production can maintain vs cost to produce. Im betting one could go to the floor and mix and match pieces out of raw production bins to make 1 saw that outputs significantly more hp than another out of the same bins but thats not the way its done... and probably make a saw that under constant use would outlast another by years before a rebuild is needed.

They also have to meet emissions requirements. Some of those requirements are counterproductive to saw life.

Im sure that some casting marks make it past QC. Even just a minor touch up beveling some of those flashings could mean a large difference to the life of the saw.

Even if they were the smartest engineers they still have bean counters.

in my humble opinion a conservative port job could certainly make a saw last longer than OEM. But thats not always the goal either.

If you can cut your sawing by an hour on a job and get paid the same enough times where your not paying your groundmen OT theres ROI there after a port job even if the saw needs a rebuild prematurely. There's less wear an tear on the user as well.


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## link (Oct 29, 2022)

I understand the interest of porting and tuning, I'm doing it myself.
But in this realm; sustainability and endurance is king.
If you temper with an OEM saw with a factory guarantee, you're on uncertain ground.
It might be better, and it might not last... 
In this particular part of the forum, I don't think you should encourage that.


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## ApePilot (Nov 4, 2022)

link said:


> I understand the interest of porting and tuning, I'm doing it myself.
> But in this realm; sustainability and endurance is king.
> If you temper with an OEM saw with a factory guarantee, you're on uncertain ground.
> It might be better, and it might not last...
> In this particular part of the forum, I don't think you should encourage that.


And just how long are the warranties? Both my stihls are only one short year (365 days) if you use their oil, otherwise their warranties are much shorter in duration. Those warranties have long ago expired by years and years. Your arguments about not porting a saw just do not add up to anything worth talking about. You seem like a bitter old small-minded man who likely made many bad choices in women, in careers, and in smoking those cancer-sticks. Otherwise you wouldn't be so concerned with someone with a sawmill wanting their saw to be maximized. Very sad you are.


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## HumBurner (Nov 5, 2022)

ApePilot said:


> And just how long are the warranties? Both my stihls are only one short year (365 days) if you use their oil, otherwise their warranties are much shorter in duration.



Last time I bought a NIB Husky, it was 6 months for professional use, and either 1-2 years if you only use their pre-mixed fuel WITH RECEIPTS TO PROVE IT


The cost of their premix negates the value of any extended warranty for a daily driver.


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## U&A (Nov 6, 2022)

ElevatorGuy said:


> @huskihl is in Michigan.


Iv used Kevin (Hhuskihi) a handful of times and he is a stand up guy that does GREAT work. I will keep going to Kevin

He also did a lot of work on my 3120xp that I use for milling.


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## Lightning Performance (Nov 17, 2022)

Stihl 041S said:


> Thank you. That probably won’t be answered.
> That was my post he quoted.
> He seems young and childish ……..a youthful knowledge……..
> 
> ...


This graph has more info in it than meets the eye.
Maybe this weekend or the next rainy evening I can catch up in this thread.

That graph shows a stable flow pattern. Notice how the power doesn't dive late in the game here in the higher RPM window. Who knows why this so and many ported simple chainsaws will not follow this pattern?


I'm betting most won't have an answer because they don't understand the why. Asking the right questions is how others can learn. Most just copycat others work, like MM, and don't have a clue about the real things going on inside the engine. If you at least grasp the basic concepts of flow your work will be better without hogged out ports or follow the "in" crowds from build to build. I've personally found the dynamic flow more important that any port size on the intake or exhaust in a dead simple two stroke piston ported engine. The total port area does not matter as much as the shape. If it has poppet valves with a cam shaft then your cross section and area becomes critical as RPMs increase. This carries over to these small engine s but not in a big way like valves do. 

You can't get out what you can't get in.


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## Lightning Performance (Nov 17, 2022)

link said:


> That's over the top buddy...


When your miracle comes maybe it will be over the top maybe not 

You really have no concept of what is going on here. Kevin and many others will give it to you straight up! These tools are not built to win races but they are built to simply work harder, pull more cutters and perform better with less issues, nothing more. Trying to explain a tool vs a toy would be a waste of my time. Explaining this to you seems to be futile.

Enjoy your day


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## ApePilot (Nov 28, 2022)

Lightning Performance said:


> This graph has more info in it than meets the eye.
> Maybe this weekend or the next rainy evening I can catch up in this thread.
> 
> That graph shows a stable flow pattern. Notice how the power doesn't dive late in the game here in the higher RPM window. Who knows why this so and many ported simple chainsaws will not follow this pattern?
> ...


I have a question that's been bugging me and I've only heard what copy-cats seem to indicate about the intake port.... that duration should be around 140 - 150 degrees. However, if you look here:

Dyno Joe's 3120xp build's torque seems to peter-out just after 8400 rpm, whereas the stock's torque curve began to nose-dive after 9200 rpm, even though of course the ported saw had far higher torque throughout the rpm range.
I have similar port numbers compared to Joe's except for my intake duration is stock at 135.8 vs Joe's 140 deg, but I also have a tighter squish (0.0228" vs joe's 0.027") and likely a bit higher true compression.

What does a longer intake duration do for the torque curve at higher rpms (8500-10,000)?

Right now the saw runs quite well and CHT hovers just below 395 deg F on 100LL at 24:1 on extended wot cuts, but I'm always looking for a bit more on top. Most of my long cuts are running at about 9600 - 9700rpm  but if I could get it up a touch higher (10,000)...?
Thanks!
-doug


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## bwalker (Nov 28, 2022)

link said:


> Im just saying; Husqvarna and Sthil have the best educated and most payed engine engineers hired in the world, and you just said that you just know so much better? Id say thats not really a wise attitude to the matter.


No they dont... the elite engineers are not working for a O P E company...


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## Sierra_rider (Nov 28, 2022)

ApePilot said:


> I have a question that's been bugging me and I've only heard what copy-cats seem to indicate about the intake port.... that duration should be around 140 - 150 degrees. However, if you look here:
> 
> Dyno Joe's 3120xp build's torque seems to peter-out just after 8400 rpm, whereas the stock's torque curve began to nose-dive after 9200 rpm, even though of course the ported saw had far higher torque throughout the rpm range.
> I have similar port numbers compared to Joe's except for my intake duration is stock at 135.8 vs Joe's 140 deg, but I also have a tighter squish (0.0228" vs joe's 0.027") and likely a bit higher true compression.
> ...



Generally speaking, too long of an intake duration can hamper low-speed power and create a motor that's slow to rev. Really too long of an intake can even induce spitback. At higher rpm, there is enough of a "pull" on it to overcome that, and help top end power. That's my generalized hack answer, one of the pros could probably elaborate better.


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## Sierra_rider (Nov 28, 2022)

I'll also add that my opinion on intake duration has changed somewhat as I've experimented. I used to keep my intake duration in the 150* range, just because I've heard that's good. I've since gone up to 160*+ on some of my builds with good success. 

My current experiment is on my 500i and how to get 160* duration after machining, w/o use of epoxy. The experiment hasn't gone perfectly, but it shows promise.


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## huskihl (Nov 29, 2022)

Sierra_rider said:


> I'll also add that my opinion on intake duration has changed somewhat as I've experimented. I used to keep my intake duration in the 150* range, just because I've heard that's good. I've since gone up to 160*+ on some of my builds with good success.
> 
> My current experiment is on my 500i and how to get 160* duration after machining, w/o use of epoxy. The experiment hasn't gone perfectly, but it shows promise.


I used to use epoxy in the intake on the 500. It made the saw rev a little quicker and it ran a shorter bar better but long bar torque and forgiveness suffered. The intake lands at 178 duration after lathe work and I leave it there now


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## link (Nov 29, 2022)

You guys talk chineese all day...


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## ApePilot (Nov 30, 2022)

huskihl said:


> I used to use epoxy in the intake on the 500. It made the saw rev a little quicker and it ran a shorter bar better but long bar torque and forgiveness suffered. The intake lands at 178 duration after lathe work and I leave it there now


Thanks guys!
I'm pretty ignorant when it comes to the new saws, like strato-charge and electronic fuel injection, at least for 2T engines. 
Does the 500i have more or less a throttle body injector system that monitors the incoming air volume through the intake? If so then I guess it pretty much relates to a carb system, except that the injection would likely occur during the actual intake impulse, rather than both intake and exhale like a carb/piston-port does?
My 3120 had been spitting a little crankcase spooge through the carb at times, but it completely stopped spitting after I had enlarged and radiused the lower transfers and piston windows. I don't see how that would have stopped the spitting, except that maybe it slightly reduced the primary compression with the removal of a very small amount of material and provided better flow, but perhaps something else was involved. 
Perhaps getting the intake duration to at least 140 deg might be helpful for higher rpm torque and not worrying about the slobbering at low and mid-rpm ranges.
178 deg of duration sounds extreme to me, but if it provides better torque at higher working rpms on that particular saw platform, hey, why not?! 
Just to verify that I'm reading you correctly, the 178 deg intake duration contributes to high-rpm torque? I would have thought that doing that would severely reduce primary compression. Maybe not? 
I'm assuming the 500i has crank-stuffers too. I'm guessing that you can get away with a bit more intake duration with a higher primary compression due in part to the stuffers?
Thanks for all the little hints.

Oh, and thank you *link* for your such valuable insights.


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## ApePilot (Nov 30, 2022)

huskihl said:


> I used to use epoxy in the intake on the 500. It made the saw rev a little quicker and it ran a shorter bar better but long bar torque and forgiveness suffered. The intake lands at 178 duration after lathe work and I leave it there now


Just did a quick calc, and found that I would have to lower my intake port by just over 8mm to achieve 178 deg duration.
What is the saw's stock intake duration?


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## Sierra_rider (Nov 30, 2022)

ApePilot said:


> Just did a quick calc, and found that I would have to lower my intake port by just over 8mm to achieve 178 deg duration.
> What is the saw's stock intake duration?


I'd have to go through my notes, but my 500i was around 168* of duration stock. I'm playing around with machined 660 pistons and my current version of the build is down to around 164* even after cutting squish and decking the cylinder.

@huskihl can comment whether I'm off-base on this, but I speculate that the long intake timing has to do with crankcase compression and the long transfer tunnels on the newer saws. At BDC, the cylinder sits very close to the cases and even has a stuffer that takes up space on the intake side. Most of the newer Stihls I've taken apart seem to have a lot of intake duration.


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## huskihl (Nov 30, 2022)

ApePilot said:


> Just did a quick calc, and found that I would have to lower my intake port by just over 8mm to achieve 178 deg duration.
> What is the saw's stock intake duration?


168-170 is stock. Opens at 84-85


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## huskihl (Nov 30, 2022)

ApePilot said:


> Thanks guys!
> I'm pretty ignorant when it comes to the new saws, like strato-charge and electronic fuel injection, at least for 2T engines.
> Does the 500i have more or less a throttle body injector system that monitors the incoming air volume through the intake? If so then I guess it pretty much relates to a carb system, except that the injection would likely occur during the actual intake impulse, rather than both intake and exhale like a carb/piston-port does?
> My 3120 had been spitting a little crankcase spooge through the carb at times, but it completely stopped spitting after I had enlarged and radiused the lower transfers and piston windows. I don't see how that would have stopped the spitting, except that maybe it slightly reduced the primary compression with the removal of a very small amount of material and provided better flow, but perhaps something else was involved.
> ...


It was more forgiving on the dogs, stayed on the pipe better with more intake. 
But the 500 is different than other saws. It doesn’t need velocity through the venturi to pull fuel. The injector is about 1” from the bore. 
I believe it has an impulse sensor, temp sensor, and crank position sensor and searches for the highest rpm in the cut via richening/leaning the mix every so often


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## huskihl (Nov 30, 2022)

Sierra_rider said:


> I'd have to go through my notes, but my 500i was around 168* of duration stock. I'm playing around with machined 660 pistons and my current version of the build is down to around 164* even after cutting squish and decking the cylinder.
> 
> @huskihl can comment whether I'm off-base on this, but I speculate that the long intake timing has to do with crankcase compression and the long transfer tunnels on the newer saws. At BDC, the cylinder sits very close to the cases and even has a stuffer that takes up space on the intake side. Most of the newer Stihls I've taken apart seem to have a lot of intake duration.


The whole top of the crankcase is a stuffer. There’s just a slot for the rod


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## ApePilot (Nov 30, 2022)

huskihl said:


> It was more forgiving on the dogs, stayed on the pipe better with more intake.
> But the 500 is different than other saws. It doesn’t need velocity through the venturi to pull fuel. The injector is about 1” from the bore.
> I believe it has an impulse sensor, temp sensor, and crank position sensor and searches for the highest rpm in the cut via richening/leaning the mix every so often


whoa! whoa! whoa!.... hold up there... Did you say 'stayed on the pipe,' hinting that you have a tuned expansion chamber on it?


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## ApePilot (Nov 30, 2022)

So, I don't see any crankshaft stuffers here. Interestingly different case top geometry, though. One transfer?


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## Lightning Performance (Nov 30, 2022)

huskihl said:


> I used to use epoxy in the intake on the 500. It made the saw rev a little quicker and it ran a shorter bar better but long bar torque and forgiveness suffered. The intake lands at 178 duration after lathe work and I leave it there now


Numbers don't lie, period.
But....
Consider who built the port window profile here. Not a guy that did 486 of one model or 2 of everything. He has years of experience now.
Doc is damn good at doing the window profile and smoothly blending it into the 260 or 360 intake runners. I think Kevin has hit his own stride now building what he thinks it wants to pull more cutters not just go fast.
Down the rabbit hole we go  

I tend to agree with this but not in all instances. Quad port vs a dual port has a tendency with good flow to not cause as much low speed spit back as a dual port does imo just by design. It should be able to handle a longer intake duration while still retaining it's manners on the low end.
Going to try answering another question someone asked on the last page.


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## Lightning Performance (Nov 30, 2022)

ApePilot said:


> I have a question that's been bugging me and I've only heard what copy-cats seem to indicate about the intake port.... that duration should be around 140 - 150 degrees. However, if you look here:
> 
> Dyno Joe's 3120xp build's torque seems to peter-out just after 8400 rpm, whereas the stock's torque curve began to nose-dive after 9200 rpm, even though of course the ported saw had far higher torque throughout the rpm range.
> I have similar port numbers compared to Joe's except for my intake duration is stock at 135.8 vs Joe's 140 deg, but I also have a tighter squish (0.0228" vs joe's 0.027") and likely a bit higher true compression.
> ...



First things first.
What is your intended purpose for this 3120?
Is it modified under those covers?
Is it stock inside?
We need facts.
Numbers vary according to how and who took them.

If you need more air/fuel maybe you need to redesign the port window and possible fix the intake runner area, maybe not.

How many cutters are you pulling in the wood?

Let's see how far this goes for something to build on. Pulling ideas and numbers out of thin air is a waste of time, period. Combinations are the only thing that works. Miss one part and you missed it all.

Kinda knew no one would try to answer my question asked earlier. It's a real simple answer imo.


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## Lightning Performance (Nov 30, 2022)

Sierra_rider said:


> I'll also add that my opinion on intake duration has changed somewhat as I've experimented. I used to keep my intake duration in the 150* range, just because I've heard that's good. I've since gone up to 160*+ on some of my builds with good success.
> 
> My current experiment is on my 500i and how to get 160* duration after machining, w/o use of epoxy. The experiment hasn't gone perfectly, but it shows promise.


Why do you suspect it needs more air in?


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## Lightning Performance (Nov 30, 2022)

Having nothing but trouble today to stay linked up in this thread. Drop link, error messages and not in service keep coming up.
My service here is just fine. Almost like someone doesn't want me posting here. That's wouldn't be the first time it's come up.


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## Sierra_rider (Nov 30, 2022)

Lightning Performance said:


> Why do you suspect it needs more air in?


I'm actually shrinking the intake duration compared to stock or what I would end up with if I just decked the cylinder with the stock piston. Stock opened at 84* BTDC, version 1 of my build opened at 80*, and version 2(which I haven't cut with yet) opens at 82*.


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## Sierra_rider (Nov 30, 2022)

ApePilot said:


> So, I don't see any crankshaft stuffers here. Interestingly different case top geometry, though. One transfer?
> View attachment 1036427


It's not a stuffer like you'd find in the crank of a 2 stroke dirtbike, but that "appendage" and the "shrouding"(for lack of a better term) around the base serve to limit crankcase volume.


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## huskihl (Nov 30, 2022)

ApePilot said:


> whoa! whoa! whoa!.... hold up there... Did you say 'stayed on the pipe,' hinting that you have a tuned expansion chamber on it?


No, just a dirt bike reference. 300lb guy on a KX65. The bike needs to be on the pipe to go anywhere


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## ApePilot (Dec 1, 2022)

Lightning Performance said:


> This graph has more info in it than meets the eye.
> Maybe this weekend or the next rainy evening I can catch up in this thread.
> 
> That graph shows a stable flow pattern. Notice how the power doesn't dive late in the game here in the higher RPM window. Who knows why this so and many ported simple chainsaws will not follow this pattern?
> ...


Here's my feeble attempt at answering this question.... 'why does this power graph not dive at higher rpms?'
Clues: it's not _all_ about port window _area_. Corners, sharp or kinda rounded, hurt flow. Square-ish corners through tunnels, corners in windows, sharp surface edges in inlet windows (inside exhaust port, lower transfer port, carb intake,etc), all hurt flow. Minimizing flow-drag is paramount to high-rpm torque, ei attempting to cram as much clean A/F charge into the combustion chamber as possible after efficient evacuation of the spent charge.
Perhaps the most efficient method of improving torque at high rpms (especially if not using a tuned expansion chamber) is to encourage smooth, laminar transfer flow. At higher rpms, the tunnel reynolds numbers become very high, creating more turbulence and therefore drag than at lower rpms, thus making far more resistance to efficiently filling the combustion chamber. The easiest way of reducing the high RNs is to slow the flow velocities down, while still providing more flow volume within the transfer duration.
How do we do all of that?
First, provide very smooth and radiused transfer entry windows (very large raduised corners) as well as smooth and open piston windows. Also provide means to smooth flow through the crankcase up into the transfers.
But if your cylinder has a dual-transfer system, the RNs will still be higher than a quad-transfer system, perhaps.
Are fingers the answer here for dual-transfer jugs? Prof. Gordon Blair mentioned this in his writings. Randy also used this to excellent effect in his 3120 build. I was surprised that Randy didn't really do much in the way of radiusing the surface corners in the lower transfers, nor did it appear that he did any massaging of the piston windows to facilitate smoother flow.
Also, by providing a larger transfer area with smooth, lower RN flow, we in effect create a longer blow-down period since the new A/F charge has a slower velocity but higher volume, something like a large open-ended water hose providing more volume but at a lower velocity vs the same hose with a tighter spray nozzle on the end.





Mastermind Meets The Husqvarna 3120


I just re-injured my wrist starting the damn thing.........I reckon the timing's a bit high. :msp_sad: I had to put a snow blower handle on mine. It will rip your fingers off if it pulls the cord back. Plus I have to pull with all my might so if just encase it does pull back. Ouch!!




www.arboristsite.com


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## ApePilot (Dec 1, 2022)

This article gives us an idea of the benefits (reduced drag and higher volume flows) of radiusing the inlets to ports such as lower transfers, exhaust port, carb inlets, etc.


http://www.profblairandassociates.com/pdfs/RET_Bellmouth_Sept.pdf


So _area_ of a port per se is not the only prerequisite for efficient flow. It's the _shape_ of the entry into that port that makes the largest difference in flow characteristics. Area is important, but is secondary to entry shape.


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## ApePilot (Dec 1, 2022)

From the same article (Blair) --
"The particle flow entering the atmosphere (reversed flow) is more pronouncedly strong for the weakest
bellmouth, i.e., the plain-ended pipe, and vice-versa for the elliptical
profile bellmouth. Indeed, it is so strong at the plain pipe end that
it has formed a toroidal vortex (smoke ring!) at the pipe end (spitback)."

This may give credence to my previous statement about eliminating the spitback through the carb. Because of the major radiusing I did to the lower transfers, the possible spitback from the transfers (w/ sharp edges) back into the case was eliminated or mitigated and therefore the case pressures were reduced before the intake phase, thus eliminating the carb spitback from the higher case pressures. I may be all wet on this topic, but maybe just damp. Something changed for the better after improving the transfer flow.


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## Bjorn T (Dec 1, 2022)

Hello, I have been thinking alot about porting and how a 2-stroke is running. I have come up to this.

crankcase compression only reaches like 10 psi. If you think about the engine running at 50-250 revolutions per second or 3000-15000 rpm, think about how long the transfers are open for each stroke. If you have an air hose pressurized to 10 psi, and could open the gate for 1/50th of a second, and that is a full stroke of the engine at idle, how much air is coming out of that hose?
The only way these engines can pump efficiently is from the energy produced by the burning mix.
At first the expanding gases push the piston down, then as the exhaust opens and the gases hit the muffler can and expand, it created a pulling effect on the rest of the cylinder, vacuum. And a lot of it. So the transfers want to open just as the pressure is changing to a vacuum for the most efficiency.

After pondering this for a bit I see this as the only way to get enough transfer to run the engine. The crankcase compression combined with a vacuum on the other side means the transfer port sees a much greater differential than just 10 psi to atmosphere


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## Lightning Performance (Dec 1, 2022)

ApePilot said:


> From the same article (Blair) --
> "The particle flow entering the atmosphere (reversed flow) is more pronouncedly strong for the weakest
> bellmouth, i.e., the plain-ended pipe, and vice-versa for the elliptical
> profile bellmouth. Indeed, it is so strong at the plain pipe end that
> ...


Wow you really went for it.

The short version is it ran out of air. Take off the air filter.

You get bonus points for three post. When you understand all the stuff you said put it in layman terms for the class to read lol.


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## Lightning Performance (Dec 1, 2022)

Bjorn T said:


> Hello, I have been thinking alot about porting and how a 2-stroke is running. I have come up to this.
> 
> crankcase compression only reaches like 10 psi. If you think about the engine running at 50-250 revolutions per second or 3000-15000 rpm, think about how long the transfers are open for each stroke. If you have an air hose pressurized to 10 psi, and could open the gate for 1/50th of a second, and that is a full stroke of the engine at idle, how much air is coming out of that hose?
> The only way these engines can pump efficiently is from the energy produced by the burning mix.
> ...


Your right it sees a big pressure hit right back down the transfer ports on stock saws.


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## Lightning Performance (Dec 1, 2022)

Sierra_rider said:


> It's already been said, but stock saws are limited by sound and emissions regulations. Power isn't their only consideration, they also have to have a quiet saw and one that runs cleanly. It seems pretty reasonable that, if you don't care about sound or emissions, you can build a saw that's optimized for power.
> 
> I'm not a guy that's a professional porter, just merely an informed "redneck," although I mostly drink hipster IPA beers or whiskey instead of gin. Just because I'm not a Stihl engineer, doesn't mean that I'm just some idiot with a dremel...I'm actually an idiot with flex shaft grinders and a lathe.
> 
> ...


Where can we buy these dark arts and idiot grinders? 
I need two please


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## Lightning Performance (Dec 1, 2022)

Stihl 041S said:


> Since you are taking that track…….why do folks that mill a lot have them ported for milling……actually milling………not just talking.


 Ported milling saws suck. They damn thing keeps killing my chain cutters every few tanks.


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## ApePilot (Dec 1, 2022)

Lightning Performance said:


> Wow you really went for it.
> 
> The short version is it ran out of air. Take off the air filter.
> 
> You get bonus points for three post. When you understand all the stuff you said put it in layman terms for the class to read lol.


Yeah, but why did it 'run out of air?' Same kind of thing would happen to an older McCulloch but at lower rpms -- but we're a bit beyond that nowdays. Taking off the air filter might help a little because of the extra drag it creates, but a bigger air filter would be better (don't worry about fitting it inside the nice, shiny cowlings). I've gone the sans filter route and I'm not doing it again.
Saying it 'ran out of air' is completely dismissing the possibility of promoting better flow up into the combustion chamber. Somehow Randy (mastermind) got there (or real close to 'there') with at least his 261 builds.
I can get far better flow, but it's difficult without a tuned expansion chamber.
As for layman terms? I think all this _is_ laymen terms. I don't know how to put it any more simply. Pretty dang succinct, don't you agree?

BjornT hasn't thought about the thermodynamics yet. As hot gasses expand from being expelled from the exhaust port, what do they do? You got it. The gasses cool a bit.
What happens when they cool? They contract in volume.
What happens when a moving gas contracts? It creates more dynamic pressure.
The typical exhaust-can on a chainsaw is not contributing to a vacuum. It's creating more back pressure than if it was not there. The whole point of the can is to attenuate the exhaust noise by cooling the gasses, creating a more constant pressure release, compared to releasing the raw pressure waves straight from the exhaust port.
Now if you subtract the can and properly design and install a tuned expansion chamber, then yes, you will create a low-pressure wave, then a high-pressure wave; this cycle begins at the time of exhaust-port opening and concludes (for the most part) before the exhaust port completely closes, when the rpm's are within the designed resonance of the pipe. Otherwise, it's not helping. Much.


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## Lightning Performance (Dec 2, 2022)

ApePilot said:


> Yeah, but why did it 'run out of air?'
> 
> Because the carb is too small on them if you port one. Ive ported the carbs and they are still too small.
> Pretty simple.
> ...


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## link (Dec 2, 2022)

Bjorn T said:


> Hello, I have been thinking alot about porting and how a 2-stroke is running. I have come up to this.
> 
> crankcase compression only reaches like 10 psi. If you think about the engine running at 50-250 revolutions per second or 3000-15000 rpm, think about how long the transfers are open for each stroke. If you have an air hose pressurized to 10 psi, and could open the gate for 1/50th of a second, and that is a full stroke of the engine at idle, how much air is coming out of that hose?
> The only way these engines can pump efficiently is from the energy produced by the burning mix.
> ...


That's a pretty thought through reply to this subject, I'm looking forwards for @huskihl reply on this, thank you sir.


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## huskihl (Dec 2, 2022)

link said:


> That's a pretty thought through reply to this subject, I'm looking forwards for @huskihl reply on this, thank you sir.


I don’t have an opinion on it. 

Bjorn and I usually agree about porting theory. I can’t prove him wrong or right and don’t really care to one way or the other, so…?


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## link (Dec 2, 2022)

OK.


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## ApePilot (Dec 3, 2022)

Lightning wrote: ... They choke once you open the mufflers and raise the transfer ports a bit. ...

I'm thinking he had a few beers too many before writing this one. Who raises the transfers in relation to the exhaust? No one that I know. Maybe they do in error? One of the big reasons that a 2T 'runs our of air,' as Lightning would say in layman terms, is because as the rpms increase, the drawdown time period shortens too much , thus the combustion pressures don't have enough 'time' to subside and evacuate through the exhaust port, and the pressure remains too high for the crankcase charge to be scavenged efficiently. Thus there is no vacuum generated by the exhaust can... it's just creates too much excess pressure. If an exhaust can did create a vacuum as does a tuned expansion pipe, then we wouldn't have need of tuned expansion pipes on other 2T engines.

The typical torque curve hits a peak at typical chainsaw working rpm, but then takes a dive, and I believe it's primarily as Lightning would suggest.... it runs out of air.... because as the rpm increases past max torque rpm, the drawdown time decreases too much and the combustion chamber pressures during drawdown remain too high for complete and efficient scavenging and therefore combustion forces don't increase at a similar rate as the increasing rpms after max torque rpm.
If we can decrease the scavanging drag as much as possible, we can extend the upward or constant trend of the torque curve a few more hundred rpms and possibly reduce the torque-dive after our extended max torque rpm. If we can LOWER the upper transfers a bit in relation to the exhaust roof, and perhaps create new 'fingers' or more transfer/boost ports (as do the 2T bikes and sleds), then we've given the combustion gasses more time to evacuate the combustion pressures to subside before we allow scavenging to start. By creating more scavenging pathways (boost ports, etc.), we help decrease the scavenging drag (lower transfer velocities) at higher rpms. That's likely why a dual transfer port engine 'runs out of air' at lower rpms compared to a quad-port saw.
At least this is what I've been trying to wrap my little pee-brain around.


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## huskihl (Dec 3, 2022)

ApePilot said:


> Lightning wrote: ... They choke once you open the mufflers and raise the transfer ports a bit. ...
> 
> I'm thinking he had a few beers too many before writing this one. Who raises the transfers in relation to the exhaust? No one that I know. Maybe they do in error? One of the big reasons that a 2T 'runs our of air,' as Lightning would say in layman terms, is because as the rpms increase, the drawdown time period shortens too much , thus the combustion pressures don't have enough 'time' to subside and evacuate through the exhaust port, and the pressure remains too high for the crankcase charge to be scavenged efficiently. Thus there is no vacuum generated by the exhaust can... it's just creates too much excess pressure. If an exhaust can did create a vacuum as does a tuned expansion pipe, then we wouldn't have need of tuned expansion pipes on other 2T engines.
> 
> ...


All depends on what the intended purpose of the saw is. Raising the transfers will raise the upper rpm torque (increasing rpm in the cut) until it doesn’t


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## ApePilot (Dec 3, 2022)

huskihl said:


> All depends on what the intended purpose of the saw is. Raising the transfers will raise the upper rpm torque (increasing rpm in the cut) until it doesn’t


So when raising the transfers, are you also raising the exhaust roof? Everything I've read and done suggests that the greater the blowdown period, the better the high rpm torque should be. Obviously the goal is to make the transfers as efficient as possible, but if the residual combustion pressure is still too high while the spent gas is exiting, no transfer flow will occur no matter how high and enlarged the transfers are made until the residual combustion pressure has been relieved to below that of the primary compression. And... and.... if the transfer roofs are too high, the residual combustion pressure will not only exit through the exhaust port, but also exit the combustion chamber through the transfers, creating a reverse flow that must be somehow reversed again for the new charge to flow in the correct direction. Attempting to reverse a contrary flow creates a lot more resistance from flow momentum, but also with more surface drag, all within the transfer tunnels. In my head, increased rpm torque requires a proper amount of blowdown time, unless you have a tuned-pipe effect that does create a vacuum that not only acts on the spent gases, but also helps pull up a fresh charge from the crankcase. A stock can does not have the proper geometry to function as a Helmholtz resonator and produce any viable vacuum,.... or does it? I'm pretty sure that the volumes of typical cans on saws are just not big enough to function as resonators. The main objective of the engineers is to make enough power while reducing radiated pressure (sound) waves to appease guberment safety and environmental agencies.
Am I incorrect? Please give us something more substantial than 'until it doesn't.'
Just trying to learn more.


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## Bjorn T (Dec 4, 2022)

Hello. I Can explain more about my Theory. But it Will take some time. My english is not good enough, so I Will need some help to get it right.


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## huskihl (Dec 4, 2022)

All depends on what the saw wants. After lathe work, I don’t know of a saw that runs better with more than factory blowdown


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## Bjorn T (Dec 4, 2022)

Hello, What I was meaning in my first post. Is that the burning mix ceratet a pulling effect in the cylinder vacuum, when the gases is leaving The cylinder out in the exhaust port. An then to the muffler.
A original muffler is restrectiv and Will not make a strong pull, But it wil help a little. A modded muffler Will help to get more pulling effekt. The muffler on the picture make a realy Strong pulling effect.
The Best exhaust system on a 2-stroke engine i a expensionchamber. It Will help pulling fuel from the crankcase and push back unburned fuel in the cylinder before the exhaust port close. But you need to have more blowdown on the engine. if you use a expensionchamber. Around 25-35 degrese. So the pipe gets time to work correct. My Hybrid have 30 degrese blowdown.  regular muffler.
Here it is with pipe.


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## link (Dec 6, 2022)

Bjorn T said:


> Hello, What I was meaning in my first post. Is that the burning mix ceratet a pulling effect in the cylinder vacuum, when the gases is leaving The cylinder out in the exhaust port. An then to the muffler.
> A original muffler is restrectiv and Will not make a strong pull, But it wil help a little. A modded muffler Will help to get more pulling effekt. The muffler on the picture make a realy Strong pulling effect.
> The Best exhaust system on a 2-stroke engine i a expensionchamber. It Will help pulling fuel from the crankcase and push back unburned fuel in the cylinder before the exhaust port close. But you need to have more blowdown on the engine. if you use a expensionchamber. Around 25-35 degrese. So the pipe gets time to work correct. My Hybrid have 30 degrese blowdown.  regular muffler.
> Here it is with pipe.




Hybrid or what, that is not the tenacious long lasting diesel kinda engine you need for milling now is it Bjonn?
That's more of a saw living on borrowed time suitable for cutting cookies in order to impress people...


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## huskihl (Dec 6, 2022)

link said:


> Hybrid or what, that is not the tenacious long lasting diesel kinda engine you need for milling now is it Bjonn?
> That's more of a saw living on borrowed time suitable for cutting cookies in order to impress people...



Keep tipping that bottle back….


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## EchoShindaiwaMakitaDolmar (Dec 6, 2022)

Expert porting of chainsaws is worth every penny- for the satisfaction alone of pi**ing off the malcontents, Nancys, and Karens. 

Owner satisfaction, increased performance, and higher productivity, are bonuses.


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## link (Dec 9, 2022)

EchoShindaiwaMakitaDolmar said:


> Expert porting of chainsaws is worth every penny- for the satisfaction alone of pi**ing off the malcontents, Nancys, and Karens.
> 
> Owner satisfaction, increased performance, and higher productivity, are bonuses.


But it's a hit and miss game, not a quality standard.
A diesel engine surpass a gas engine in both torque and hours, why is that? 
Relative low rpm does not make a pretty HP chart, only long lasting reliable engines.


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## huskihl (Dec 9, 2022)

link said:


> But it's a hit and miss game, not a quality standard.
> A diesel engine surpass a gas engine in both torque and hours, why is that?
> Relative low rpm does not make a pretty HP chart, only long lasting reliable engines.


There’s guys around who can port your saw and actually make it slower. You could look into that.

Longevity


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## dmb2613 (Dec 9, 2022)

I dont know She it from shanola about porting, but I do know a 034S will cut a circle around a 036 wink lol


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## link (Dec 14, 2022)

huskihl said:


> There’s guys around who can port your saw and actually make it slower. You could look into that.
> 
> Longevity


I know you will make it better buddy. I just don't follow the popular tunes...


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## ApePilot (Dec 15, 2022)

link said:


> I know you will make it better buddy. I just don't follow the popular tunes...


Perhaps, link, you should go take a nice, warm bubble bath and let the adults discuss these things.


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## ApePilot (Dec 15, 2022)

Bjorn T said:


> Hello, What I was meaning in my first post. Is that the burning mix ceratet a pulling effect in the cylinder vacuum, when the gases is leaving The cylinder out in the exhaust port. An then to the muffler.
> A original muffler is restrectiv and Will not make a strong pull, But it wil help a little. A modded muffler Will help to get more pulling effekt. The muffler on the picture make a realy Strong pulling effect.
> The Best exhaust system on a 2-stroke engine i a expensionchamber. It Will help pulling fuel from the crankcase and push back unburned fuel in the cylinder before the exhaust port close. But you need to have more blowdown on the engine. if you use a expensionchamber. Around 25-35 degrese. So the pipe gets time to work correct. My Hybrid have 30 degrese blowdown.  regular muffler.
> Here it is with pipe.



Seems to me, that divergent piped saw that you have pictured at the bottom of your post would need an extra long blowdown simply because the divergent-only pipe does create a low-pressure (suction) exhaust, but does nothing to push back the charge that it would exteract out of the cylinder along with the spent charge. That's why a tuned pipe requires a convergent cone as well, as you likely well know. A properly tuned pipe will allow the engine to respirate far better at the pipe's designed rpm's than without, but, if I understand the dynamics, the porting numbers for a tuned pipe doesn't change compared to a non-tuned exhaust.
What are your beliefs Bjorn?


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## Bjorn T (Dec 16, 2022)

ApePilot said:


> Seems to me, that divergent piped saw that you have pictured at the bottom of your post would need an extra long blowdown simply because the divergent-only pipe does create a low-pressure (suction) exhaust, but does nothing to push back the charge that it would exteract out of the cylinder along with the spent charge. That's why a tuned pipe requires a convergent cone as well, as you likely well know. A properly tuned pipe will allow the engine to respirate far better at the pipe's designed rpm's than without, but, if I understand the dynamics, the porting numbers for a tuned pipe doesn't change compared to a non-tuned exhaust.
> What are your beliefs Bjorn?


Hello, I am not an expert. But if you port a cylinder for regular muffler or a tuned pipe. The porttiming numbers will be way different. 

The big changes is blowdown.


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## Bjorn T (Dec 16, 2022)

ApePilot said:


> Seems to me, that divergent piped saw that you have pictured at the bottom of your post would need an extra long blowdown simply because the divergent-only pipe does create a low-pressure (suction) exhaust, but does nothing to push back the charge that it would exteract out of the cylinder along with the spent charge. That's why a tuned pipe requires a convergent cone as well, as you likely well know. A properly tuned pipe will allow the engine to respirate far better at the pipe's designed rpm's than without, but, if I understand the dynamics, the porting numbers for a tuned pipe doesn't change compared to a non-tuned exhaust.
> What are your beliefs Bjorn?


Hello. I Can give you thre exampels, 1 Woods porting, with muffler. Exhaust widened to 65% of the Bore and 154 degrese of duration, intake widened and lowered so 160 dregrese of duration, transfers adjusted, size and aiming. 120 degrese of duration

2, with tuned pipe. Exhaust 60% of the Bore, 170 degrese of duration. Intake widened and lowered so 152 degrese of duration. Transfers adjusted size and aiming. 110 degres of duration. This Will give 30 degrese blowdown, and that Will give the pipe time to work correct.

3. race saw with pipe, exhaust same as number 2. Intake widened Max, as mutch as possible, depends on the piston skirt. Lowered to 170 degrese of duration. Full circle crank, to raise the crankcase compression. Transfers modified, opened and aimed for good flow, 110 degrese of duration and bigger carburator, this porting give you 30 degrese of blowdow, and 40 degrese of crankcase compression, good fore high rpm cut.

fore work saws I like 45-50 degrese of crankcase compression or more, that give you a snappy saw. And dont raise the exhaust more than 102 degrese, to have some tourque fore long bars.
this is just general porting Numbers. And it Will not be perfect on all saws. Mostley because there is many different modells of transferports.


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## Lightning Performance (Dec 16, 2022)

huskihl said:


> There’s guys around who can port your saw and actually make it slower. You could look into that.
> 
> Longevity


So your known for making them fast, yes?... sooo how slow can you make my saw? I need it to last until the next millenia, please


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## Bjorn T (Dec 16, 2022)

Lightning Performance said:


> So your known for making them fast, yes?... sooo how slow can you make my saw? I need it to last until the next millenia, please


This Will work good. https://www.videoman.gr/sv/44237


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## huskihl (Dec 16, 2022)

Bjorn T said:


> This Will work good. https://www.videoman.gr/sv/44237


Not really known for anything. I just show the way it was vs the way it is now I guess


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## ApePilot (Dec 17, 2022)

Bjorn T said:


> Hello, I am not an expert. But if you port a cylinder for regular muffler or a tuned pipe. The porttiming numbers will be way different.
> 
> The big changes is blowdown.


I'm going to have to disagree with that statement. The tuned pipe is _tuned_ to the porting, not the other way around. Obviously, there would be advantages to optimizing both the porting and the pipe to each other, but the porting numbers would still be not much different. Take a look at the Radne Raket 120 kart engine. It is exactly derived from the Husqvarna 3120xp. Same OEM piston, same OEM crank, same OEM cylinder, same ignition timing (which should actually be retarded for better high-rpm torque). The only real differences to the 3120xp saw is a redesigned heavier-duty crankcase to facilitate bolting the engine to a frame, the clutch sprocket, and the _tuned_ pipe. It develops 14 hp at 9000 rpm compared to a stock 3120xp saw of 8 hp at 10,000 -- all because of the _tuned_ pipe, nothing more.


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## Bjorn T (Dec 18, 2022)

ApePilot said:


> I'm going to have to disagree with that statement. The tuned pipe is _tuned_ to the porting, not the other way around. Obviously, there would be advantages to optimizing both the porting and the pipe to each other, but the porting numbers would still be not much different. Take a look at the Radne Raket 120 kart engine. It is exactly derived from the Husqvarna 3120xp. Same OEM piston, same OEM crank, same OEM cylinder, same ignition timing (which should actually be retarded for better high-rpm torque). The only real differences to the 3120xp saw is a redesigned heavier-duty crankcase to facilitate bolting the engine to a frame, the clutch sprocket, and the _tuned_ pipe. It develops 14 hp at 9000 rpm compared to a stock 3120xp saw of 8 hp at 10,000 -- all because of the _tuned_ pipe, nothing more.


Hello. There are many ways to porting and building pipes. If you have 10 porters and 10 Pipe builders. To build 10 saws of the same modell. None Of the saws Will be exaktly the same. 

most Factory build 2-stoke high performance engines, like dirt bikes have a blowdown of 30-35 degrese. If some smart guy have been able to build a pipe for short blowdown. And make many HP extra, thats a big bonus. But my head or calculation programs on the internet, is not smart enought to do it.


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## ApePilot (Dec 18, 2022)

Bjorn T said:


> most Factory build 2-stoke high performance engines, like dirt bikes have a blowdown of 30-35 degrese. If some smart guy have been able to build a pipe for short blowdown. And make many HP extra, thats a big bonus. But my head or calculation programs on the internet, is not smart enought to do it.


Any shorter of blowdown, and the spent charge will be pushed into the transfers and down into the case. I've seen the results of this.... black spooge in the case and spitting out the carb. You can't generate a negative pressure wave immediately after the exhaust port begins to open. It takes a few msec for that negative wave to get back to the exhaust port and help suck the exhaust and some of the fresh charge out. Therefore, you have to time the blowdown for the expected rpms to achieve and for the negative pressure wave to return to help suck the fresh charge up from the case. The greater the rpm's the longer (in degrees) the blowdown should be. If the transfers opened too early, like you are suggesting, there would be a flow reversal within the transfers that would take even more time to correct and the transfer flow efficiency would be squandered away. There's a reason most of today's 2T bikes have power valves.... it's to increase the blowdown time as rpm's rise to help match the return negative pressure wave of the pipe to allow for a larger range of rpm's that the pipe can be in tune with.
Even without a tuned pipe, blowdown should be matched to the desired rpm range, IE, the higher the rpm, the longer the blowdown should be. If you're raising the transfers in relation to the exhaust roof, you're then limiting the upper rpm range of power. You have to allow the exhaust to evacuate and allow enough time for combustion chamber pressure reduction before you open the transfers.
The only reason I can think for raising the transfers in relation to the exhaust port is to achieve low rpm torque, but that is exactly opposite of what a 2T is best used for, unless you merely like a throttle-snappy saw that peters-out just above mid-range. That would be a waste of displacement and saw mass.

The big question in my mind, is what would appreciably increasing a stock piston ported intake duration actually accomplish? Would it help Mid-range torque? Higher rpm torque? There would be a point at which any larger a duration would reduce primary compression. I'm guessing that the name of the game is to help cram as much fresh charge as possible into the case, and the momentum of the incoming charge from the carb would continue into the case even after a positive pressure is achieved, at a certain rpm range at least. Below that range, the extra duration may not be a benefit. Does this sound about right?

I think we have a good productive discussion going now.


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## huskihl (Dec 18, 2022)

ApePilot said:


> Any shorter of blowdown, and the spent charge will be pushed into the transfers and down into the case. I've seen the results of this.... black spooge in the case and spitting out the carb. You can't generate a negative pressure wave immediately after the exhaust port begins to open. It takes a few msec for that negative wave to get back to the exhaust port and help suck the exhaust and some of the fresh charge out. Therefore, you have to time the blowdown for the expected rpms to achieve and for the negative pressure wave to return to help suck the fresh charge up from the case. The greater the rpm's the longer (in degrees) the blowdown should be. If the transfers opened too early, like you are suggesting, there would be a flow reversal within the transfers that would take even more time to correct and the transfer flow efficiency would be squandered away. There's a reason most of today's 2T bikes have power valves.... it's to increase the blowdown time as rpm's rise to help match the return negative pressure wave of the pipe to allow for a larger range of rpm's that the pipe can be in tune with.
> Even without a tuned pipe, blowdown should be matched to the desired rpm range, IE, the higher the rpm, the longer the blowdown should be. If you're raising the transfers in relation to the exhaust roof, you're then limiting the upper rpm range of power. You have to allow the exhaust to evacuate and allow enough time for combustion chamber pressure reduction before you open the transfers.
> The only reason I can think for raising the transfers in relation to the exhaust port is to achieve low rpm torque, but that is exactly opposite of what a 2T is best used for, unless you merely like a throttle-snappy saw that peters-out just above mid-range. That would be a waste of displacement and saw mass.
> 
> ...


Most of that might sound good to you or look good on paper, but doesn’t work well in a saw with a can muffler. 

Most piped race saws have 26-32° blowdown, where muffler race saws are more like 24-28°. Woods ported saws need torque so the exhaust is typically lower, and raising the transfers after lathe work adds more torque yet, resulting in higher rpm while cutting. Some saws I’ve had luck adding a few degrees blowdown and some run the best for me with 6-8° less. 

There’s no one-recipe-fits-all type stuff. And very little of the stuff written about piped motorcycles works in a saw. Bore/stroke ratio is too different


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## ApePilot (Dec 19, 2022)

huskihl said:


> Most of that might sound good to you or look good on paper, but doesn’t work well in a saw with a can muffler.
> 
> Most piped race saws have 26-32° blowdown, where muffler race saws are more like 24-28°. Woods ported saws need torque so the exhaust is typically lower, and raising the transfers after lathe work adds more torque yet, resulting in higher rpm while cutting. Some saws I’ve had luck adding a few degrees blowdown and some run the best for me with 6-8° less.
> 
> There’s no one-recipe-fits-all type stuff. And very little of the stuff written about piped motorcycles works in a saw. Bore/stroke ratio is too different


I now understand where you're coming from, I think. It makes more sense now than when you previously indicated that you raise the transfers but didn't provide a description of the resultant relative blowdown.

My 3120 currently is set up as:
Blowdown: 19.6 deg
Exhaust duration: 164.02 deg, opens at 97.991 deg atdc
Transfer duration: 124.79 deg, opens at 117.6 deg atdc
Intake duration: 135.8 deg, closes at 67.88 deg atdc
true compressible volume: 86.207 cc
compressed volume: 9.64 cc
squish: 0.58mm
Compression ratio: 8.943:1

-- it could likely use more blowdown, but I'm unwilling at this point to reduce it's displacement (raising the exhaust roof) to increase blowdown time. But perhaps it wouldn't hurt.
Blowdown would be longer if Transfer duration was reduced to 120 deg ( for a 22 deg blowdown) but I'm hesitant about using epoxy-fill, likely not a reliable option.

However, it's current intake duration is anemically short (135.8 deg.) compared to others' figures. It probably should be opened up to around 140 deg or possibly more. But I'd like to better understand what advantages a longer intake duration would provide.


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## link (Dec 20, 2022)

ApePilot said:


> Perhaps, link, you should go take a nice, warm bubble bath and let the adults discuss these things.


Hehe... just outta curiosity - how old are you buddy? 
I would love a nice bubble bath though - I guess I'd have to make it happen myself...


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## Lightning Performance (Jan 4, 2023)

ApePilot said:


> I now understand where you're coming from, I think. It makes more sense now than when you previously indicated that you raise the transfers but didn't provide a description of the resultant relative blowdown.
> 
> My 3120 currently is set up as:
> Blowdown: 19.6 deg
> ...


It appears your quoting known measurements for online calculators not a degree wheel. Am I correct?
If so this very well may or may not match the inside of your acual cylinder.


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