# Modifying Strato/X-Torq saws...



## MCW (Apr 8, 2011)

Hi gents.

Just a quick question from a mechanically handicapped saw user.
There have been a number of strato style saws being modded on AS lately and I have some questions...

Do they lose their fuel saving efficiency once modded?

For example, will a modified 372 X-Torq still be roughly 20% more fuel efficient than a similarly modded 372XP?

After modifying can they still be classed as a strato type saw or are many of these features ground away in the process?

Thanks for any replies and my understanding of how these more modern saws work is limited to the knowledge that they still run on 50:1 fuel, just for longer 

Matt


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## sunfish (Apr 8, 2011)

After following most of the strato builds here, I've come to the conclusion that it might be best to leave them stock, or just do a MM and be done with it. I'm sure the porting dudes will figure something out though.


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## flyank (Apr 8, 2011)

"mechanically handicapped saw user"

- sorry, had to chime in off topic here... I love that quote.


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## mweba (Apr 8, 2011)

Depends on how they are modified. On my 372 xt, the first porting I did to it, the strato splitter was removed in order to "stuff" the strato ports with fuel. In this case, the initial charge entering the combustion chamber was mix instead of fresh air. This configuration was by no means fuel efficient.

The way my xt stands now, the strato function was left alone. Fuel mileage was retained. The current cylinder is conventional woods ported.

Hope that ramble helped.


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## MCW (Apr 8, 2011)

sunfish said:


> After following most of the strato builds here, I've come to the conclusion that it might be best to leave them stock, or just do a MM and be done with it. I'm sure the porting dudes will figure something out though.



That was my initial impression too 



flyank said:


> "mechanically handicapped saw user"
> 
> - sorry, had to chime in off topic here... I love that quote.



I'll even let you use that quote if you'd like 



mweba said:


> Depends on how they are modified. On my 372 xt, the first porting I did to it, the strato splitter was removed in order to "stuff" the strato ports with fuel. In this case, the initial charge entering the combustion chamber was mix instead of fresh air. This configuration was by no means fuel efficient.
> 
> The way my xt stands now, the strato function was left alone. Fuel mileage was retained. The current cylinder is conventional woods ported.
> 
> Hope that ramble helped.


 
Thanks for the ramble and yes it helped  The splitter is what I have seen being removed in most mods on AS which is why I questioned the fuel economy. I gathered that by modifying it too extensively that any fuel savings from the strato design would be basically null and void.


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## mweba (Apr 8, 2011)

sunfish said:


> After following most of the strato builds here, I've come to the conclusion that it might be best to leave them stock, or just do a MM and be done with it. I'm sure the porting dudes will figure something out though.


 
Many saw builders work these over with great success. AS in the world of porting is a small percentage of the examples in the field. One very public bad experience does not necessarily mean this is the norm. Gains are there to be made and unfortunately strato is the world we live in.


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## MCW (Apr 8, 2011)

mweba said:


> Many saw builders work these over with great success. AS in the world of porting is a small percentage of the examples in the field. One very public bad experience does not necessarily mean this is the norm. Gains are there to be made and unfortunately strato is the world we live in.



Do the gains negate the fuel efficiency though if heavily modified? If so then do you still see any benefits over a non strato saw?

P.S. I still haven't got a good grasp on the concept of strato


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## mweba (Apr 8, 2011)

Give it a go in another description. Completely ignore all the extra runners, splitters and transfers. 
In essence, all an strato does is "chase" or "scavenge" the burnt charge out with fresh air using two extra ports that open before the mix transfers. By doing this, fresh air is lost out the exhaust instead of unburnt mix making the system more efficient. A common misconception is the a strato runs leaner due to using less fuel. This is not the case, it just wastes less out the exhaust. The charge being burnt is the same. This is how they get the clean emissions. 

Now there are variances already to this design....372xt does it a little different with tranfer timing but the overall concept is the same.

Really nothing wrong with a starto IMO, just a new challenge.

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## CentaurG2 (Apr 8, 2011)

Sharp chain and efficient cutting techniques are the only mods you really need. I have yet to see a decent study that shows greater or less fuel efficiency between stratos and regular saws let alone heavily modified units. We are just asked to believe by the manufactures that stratos are more fuel efficient.


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## mweba (Apr 8, 2011)

CentaurG2 said:


> Sharp chain and efficient cutting techniques are the only mods you really need. I have yet to see a decent study that shows greater or less fuel efficiency between stratos and regular saws let alone heavily modified units. We are just asked to believe by the manufactures that stratos are more fuel efficient.


 
I agree that the best and most overlooked "mod" is proper chain maint. 

All manufacturers rely on convincing the consumer there product is better. Most can be won over by a simple statement rather than science.

Having run both the 372xt and OE side by side on many jobs. The Xt is more fuel efficient, twenty percent.....not sure but either way it gets filled less no matter the operator. 

Just my real world experience, others may differ.


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## Chris J. (Apr 8, 2011)

CentaurG2 said:


> Sharp chain and efficient cutting techniques are the only mods you really need.* I have yet to see a decent study that shows greater or less fuel efficiency between stratos and regular saws let alone heavily modified units.* We are just asked to believe by the manufactures that stratos are more fuel efficient.




I have no idea about a "decent study," but I'll trust the word of the AS members who say the strato saws are fuel sippers.

MCW, judging from your posts, I somehow doubt that you're completely "mechanically handicapped." :cool2:


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## sunfish (Apr 8, 2011)

Thanks mweba!

I am actually looking forward to getting a strato saw at some point. The reports so far have been positive, some very positive.


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## MacLaren (Apr 8, 2011)

So,what I gather is that they can be ported and most have no problems porting them. Thats good to know.


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## blsnelling (Apr 8, 2011)

I have ported quite a few strato saws, most of them with great success. I treat each model differently. The MS261 is one that I completel remove all strato clean air from. All of the air is charged with fuel. I tried it leaving the strato system intact, and it didn't respond like I wanted. Most other models I leave intact. This would include the little Ryobi/Redmax saw, which is the strongest 40cc class saw I've ever ported. The MS441 and MS362 also respond very well to porting and leaving the strato technology intact. The only saw I've had reliability issues with was the 372XP XT, and I removed it's strato stuff since it was designed VERY similiarly to the MS261. I've only done the one and did not try it leaving the strato still functional. The bottom line is that strato saw respond very well to porting. If the strato functionality is left functional, it can't help but save on fuel. One case that helps prove this, is that the MS261 H needle must be backed out 2 1/2 turns once I'm done with my mods. That's how much more fuel it needs to be rich enough. Fortunately, the carb still responds very well to adjustments at that point.


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## blsnelling (Apr 8, 2011)

hillbilly22 said:


> So,what I gather is that they can be ported and most have no problems porting them. Thats good to know.


 
That is correct.


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## CentaurG2 (Apr 8, 2011)

mweba said:


> I agree that the best and most overlooked "mod" is proper chain maint.
> 
> All manufacturers rely on convincing the consumer there product is better. Most can be won over by a simple statement rather than science.
> 
> ...


 
So with higher efficiency (assuming the take size is equal), do you get more wood cut per tank or do you get a longer run time per tank or both?? I tried to get my hands on a 372xt autotune earlier this year but the dealer and I did not see eye to eye. I will eventually get one and give it a go against a non-strato 372xp. 

Only strato I do have is a redmax ebz8001 and there is nothing fuel efficient about that thing. It just plain drinks fuel. Displacement is 71.9cc, fuel capacity 77.7oz, run time per tank about 1 hour at WOT under load. Husky 372xp, displacement 71cc, fuel capacity 26.08oz, run time per tank at WOT under load is about 18 to 20min. I don’t see a lot savings between these two machines real world. Yup its like comparing apples to pine nuts but it is at least some numbers to work off.


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## MacLaren (Apr 8, 2011)

This is a good thread. Thanks for posting it Matt. Im glad MWEBA got in there and gave us his input. Know, goin on what MWEBA has said I may just have to get one of these babies and have it ported. That may be a while though as I may be gettin a 90cc already...lol!!......CAD is for real!


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## mweba (Apr 8, 2011)

CentaurG2 said:


> So with higher efficiency (assuming the take size is equal), do you get more wood cut per tank or do you get a longer run time per tank or both?? I tried to get my hands on a 372xt autotune earlier this year but the dealer and I did not see eye to eye. I will eventually get one and give it a go against a non-strato 372xp.
> 
> Only strato I do have is a redmax ebz8001 and there is nothing fuel efficient about that thing. It just plain drinks fuel. Displacement is 71.9cc, fuel capacity 77.7oz, run time per tank about 1 hour at WOT under load. Husky 372xp, displacement 71cc, fuel capacity 26.08oz, run time per tank at WOT under load is about 18 to 20min. I don’t see a lot savings between these two machines real world. Yup its like comparing apples to pine nuts but it is at least some numbers to work off.


 
Redmax to 372 has to many variables. Really all I can add for educated info is the comparison side by side 372 old and new. The XT gets the same work done with less fuel and less down time...if not more done because of less down time. 

As you stated earlier though, chains can make more of a difference with speed of production....for that matter, its hard to get anyone to work for you these days that stays consistently productive LOL


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## Terry Syd (Apr 8, 2011)

I left my strato function intact when I ported it. I'm glad when the tank finally runs dry, I can take a break/collapse.

The strato saws have a much greater time/area for the intake cycle. It is not just the intake port that feeds the crankcase, but the transfer ports as well. A conventional two-stroke is limited by the width of the intake port. 

The increase in the area of the intake cycle allows the strato to 'gulp' the mixture a lot quicker. You don't need as much intake timing to fill the crankcase, that translates into an engine with more torque.


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## spike60 (Apr 8, 2011)

blsnelling said:


> The only saw I've had reliability issues with was the 372XP XT, and I removed it's strato stuff since it was designed VERY similiarly to the MS261. I've only done the one and did not try it leaving the strato still functional.



Some people here on the site are eager to step on someones toes, and some are so afraid of doing so, that they are afraid to say what they are thinking. I'm neither, so.............

Brad, the only "issues" the 372XT has had is your porting. :msp_smile: 

I can't sit here quietly if there's going to be any attempt at all to shift the spotlight regarding that failure to the saw itself. Chipmonger's saw is the only 372XT failure that I know of. 

You know I'm not one of those guys that will play a game of "gotcha!" and sit here and try to nail you to the cross about it. Just a simple mistake, that any of us can make. I'm sure we all have a few things in the corner of the shop that we've screwed up. 

But recall, you told me personally that you went too far with the exhaust port, and that you tried to correct that error, and save the cylinder, by lowering the port. It worked for a while, but of course the original mistake was still there, and the ring caught a second time. It's not a big deal; just a little "ooops!" that any of us can make from time to time. 

There will be no damage to your image or credibility to simply say, "Yeah, I kind of over did it with that one and screwed it up." 

You did all the right things for Chipmonger. You paid for the first piston, and you paid for the replacement XPW P&C. I'm not sure how many builders would have done the same. So, do another "right thing" regarding that saw, and just admit to a simple porting error. 

But any suggestion that there might be something wrong with the design of the 372XT is not cool at all, and I won't sit here without responding. A lot of members look up to your opinion on things, and they may read a comment like the one I quoted you and conclude that the 372XT is a saw they should steer clear of. That is certainly not the case, as those things have been extremely reliable. 

I was saving an original 372 in the box, that I figured I might want to be able to pull out a few years from now. After running the XT, I decided to sell the original I had been saving. Boys, the XT is one good saw.


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## blsnelling (Apr 8, 2011)

Terry Syd said:


> The strato saws have a much greater time/area for the intake cycle. It is not just the intake port that feeds the crankcase, but the transfer ports as well. A conventional two-stroke is limited by the width of the intake port.
> 
> The increase in the area of the intake cycle allows the strato to 'gulp' the mixture a lot quicker. You don't need as much intake timing to fill the crankcase, that translates into an engine with more torque.


 
I don't follow. All of the fuel charge has to come through that one tiny intake port. IMO, it's one of the design characteristics that limits the output of most strato saws. This is why the MS261 requires gutting of the strato stuff to get it to it's performance potential.


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## blsnelling (Apr 8, 2011)

spike60 said:


> Some people here on the site are eager to step on someones toes, and some are so afraid of doing so, that they are afraid to say what they are thinking. I'm neither, so.............
> 
> Brad, the only "issues" the 372XT has had is your porting. :msp_smile:
> 
> ...


 
I appreciate your style I ported the exhaust on that 372XP XT to 70% of bore with, as measured straight across. That's no wider than I port any saw, percentage wise. I port bigger saws to the same width with no ill effects. For some reason, it seems that's too wide for this particular model. There was no damage to the cylinder in the first go around that would have caused the second failure, and the flat port floor was fixed. The first was entirely due to the flat port floor. The second one is anyones guess. I honestly do not know why it failed.


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## Terry Syd (Apr 8, 2011)

"I don't follow. All of the fuel charge has to come through that one tiny intake port. IMO, it's one of the design characteristics that limits the output of most strato saws."

When I first looked into the guts of a strato, like you, all I initially saw was the small intake port. However, I tried a few things. I tried disconnecting the strato butterfly to see how it affected the power and quickly realised that the engine needed the strato air to make any power.

I also came to the conclusion that the wonderful graphics that were done for advertising the strato were not representative of what was actually going on in the engine. Yes, the strato air charge in the top of the transfer ports would get the exhaust gases moving out of the cylinder and some of it would be lost out the exhaust. However, a good portion of it remained in the cylinder.

That remaining air in the cylinder would become mixed due to turbulence with the air/fuel mixture that was coming in behind it. During 'squish' I expect that there is fairly uniform mixing in the combustion chamber.

In other words, we are talking about an intake cycle, that is, the gross amount of air/fuel and the strato air. We want to maximise the flow of both portions of the intake cycle to get the most power.

Going back to the picture you posted. The strato air comes in through the two strato ports - now here is the biggie - the cutaway on the piston feeds the air to the two transfer ports (on your picture it looks like it feeds four ports).

Do the math. Measure the width of the intake port. Now measure the width of the transfer ports. Add them all together and that is the total width of your intake.

Whereas a conventional two-stroke may have an intake that is 70% of bore, a strato can have over 100% of bore (mine is 95% of bore). Further, the intake and the transfer ports are flat, that means they open NOW. There is no requirement for the lower edge of the intake port to have a curve in it to keep from snagging the intake skirt.

I also experimented and found that matching the intake and strato timing gave me the best power. By having both intake and strato timing the same, it maximised base compression.

Since most (if not all) stratos are coming with strato timing that is longer than the intake timing, IMO the first mod should be to match the timing of the ports. If you determine that you need a bit more timing, then BOTH the intake and strato timing need to be moved.

The strato port flow also needs to be maximised. I found that I couldn't do anything to the ports in the jug, but the piston cutaway was restricting the flow (especially at TDC). I did all my porting on the strato flow by reworking the piston cutaway.


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## blsnelling (Apr 8, 2011)

Let me make one thing clear. In no way am I saying that the 372XP XT is a bad saw. By all accounts, it's a great saw. However, for those that port saws, there are a couple things to pay special attention to. First, make the exhaust port concave. Fortunately, there's pleny to piston skirt to allow that. Second, be very conservative on your exhaust port width. I recommend more along the lines of 60% of bore diameter, measured straight across the port.


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## blsnelling (Apr 8, 2011)

I understand what you're saying Terry. But, those strato ports aren't bringing fuel into the cylinder. Fuel is what goes bang. The more fuel an engine con efficiently burn, the more power it's going to make. On all of the stratos that I have ported, I have found room for improvement in the strato ports in the cylinder itself. I do not mod the piston at all. The can be ported like any transfer port. 

I went through all the varies recipes in finding what works on the MS261. I tried removing the butterfly in the carb. I tried removing the divider right after the carb. It wasn't until I completely removed all dividers that the saw made the power it's capable of. In essence, I turned the strato ports into extra transfer ports, carrying more burnable fuel to the cylinder. A 261 without these mods will not make the same power. I tried.


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## parrisw (Apr 8, 2011)

Matt, is your new name Handi? 




LOL, your just being Humble I'm sure. I wouldn't think for a minute your handicap with saws. I've still never worked on a Strato saw, can't wait too though.


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## blsnelling (Apr 8, 2011)

Let me add, some stratos won't allow you to make the mods I did to the 261. Saws like the 362 and 441 I simply take what they'll give me. I see no practical way to feed fuel to 100% of the fuel charge.


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## parrisw (Apr 8, 2011)

blsnelling said:


> Let me make one thing clear. In no way am I saying that the 372XP XT is a bad saw. By all accounts, it's a great saw. However, for those that port saws, there are a couple things to pay special attention to. First, make the exhaust port concave. Fortunately, there's pleny to piston skirt to allow that. Second, be very conservative on your exhaust port width. I recommend more along the lines of 60% of bore diameter, measured straight across the port.


 
Brad, I'm sure there are a bunch of guys thinking, I'm glad it happened to him and not me! It was a big learning experience for you and all of us. No worries, we're all glad you let us know what your findings were.


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## albert (Apr 8, 2011)

If you pull the divider, then most of the extra air fuel mix that goes through the strato ports will go straight out of the muffler, due to the strato design. I see that as a big waste, and the exhaust probally will stink and burn your eyes worse than a convential 2 stroke. I think most of the pro strato saws run pretty slick out of the box. And Spike is right about the 372xt, it's a very strong running and efficient saw out of the box. IMO it don't see the need to mess with a good thing.


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## Terry Syd (Apr 9, 2011)

Brad, all these various stratos are a bit different and take a slightly different approach to each of them. As I said 'on my saw' I couldn't make the strato ports any bigger. This is a Husky 450 that is based upon the 445 - the engineers had trimmed every bit of port work they could to open it up. In fact, the strato butterfly was a big 16mm, but the manifold was only 13.5mm. It became clear why it was only 13.5mm after I calculated the area of the strato ports in the cylinder, that's all it needed.

However, the piston did partially block the ports in the cylinder, so I reworked the piston so that the whole system could flow like it was designed to. I even trimmed back the ends of the pin boss so that the air could get past it.

Back to the fuel issue. It is real easy to get more fuel in a engine, just richen the mixture. The real trick is to get more air in the engine in order to burn the fuel - think super or turbo charging as a case on point.

The strato port is part of the intake cycle. If you can improve upon the flow of the strato system, you can increase the amount of air available for combustion. As I stated, there appears to be complete mixing of whatever is available in the cylinder by the time of combustion.


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## weimedog (Apr 9, 2011)

Terry Syd said:


> Back to the fuel issue. It is real easy to get more fuel in a engine, just richen the mixture. The real trick is to get more air in the engine in order to burn the fuel - think super or turbo charging as a case on point.
> 
> .


 

Bingo..that was what I was looking for. And this also means the the actual carburation or mixing of the mixture(s) is done in the combustion chamber. Most are assuming that a conventional ratio of gas air must come from that intake port directly down stream from the carb and what your saying is if your smart you use ALL the x-sectional area available to get as much air in as possible and then add more fuel thru the carb to compensate....this vs. trying to hack the ports up stream to take out the butter fly and have all the carburation done in a conventional way. My question is along the lines of does all that fresh air towards the exhaust side have an effect on lubrication?

Also I wonder if this is why the more I richen my 455, the more power it seems to have....now I have to wonder what just simply a muffler mod would do plus adding more fuel!

Based on this it would seem there is power to be had by simply a muffler mod and working of the carburetor side of things. I think I understand in a theoretical way your thoughts on the transfer timing...still wrestling on how to apply though. Thank you for the insight! I'm really wondering how this will shake out when some of the more "out of the box" thinkers in the saw performance community start absorbing what your just articulated...


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## MCW (Apr 9, 2011)

Hey thanks for all the inut guys and keep it coming. Some very interesting talk. Thanks for the vid too demonstrating the strato engines.
Although I don't have two similar model saws side by side I can say that my 261 does indeed run forever on a tank of fuel and would have to cut 25% more wood than my 5100-S per tank. I don't know what the tank sizes are but the 261 is one of those saws that just grows on you every time you use it. It's got that much torque that I'm now running the same aggressive 20" 3/8" chains on it that are normally reserved for the modded Dolmar 7900's...



Chris J. said:


> MCW, judging from your posts, I somehow doubt that you're completely "mechanically handicapped." :cool2:



When in comes to pulling a cylinder off or fixing something all good. Mention port timings or "strato" and I am 100% medicated and certifiable...



parrisw said:


> Matt, is your new name Handi?



Why yes it is Will  Handimatt...



parrisw said:


> LOL, your just being Humble I'm sure. I wouldn't think for a minute your handicap with saws.



I'm not handicapped using saws but I certainly feel handicapped when you smarter guys start talking porting and timing. I might as well be sitting down listening to a quantum physics lecture...


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## Chris J. (Apr 9, 2011)

MCW said:


> ....
> 
> When in comes to pulling a cylinder off or fixing something all good. Mention port timings or "strato" and I am 100% medicated and certifiable...
> ...
> ...


 

I know the feeling:   :bang: :msp_blink:.


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## Terry Syd (Apr 9, 2011)

"I think I understand in a theoretical way your thoughts on the transfer timing...still wrestling on how to apply though."

weimedog, if you are referring to matching the strato and intake timing, then on your saw it is very easy. All you have to do is pull one of the covers off the transfer ports and watch when the strato cutaway appears over the bottom of the transfer port - that's when the strato timing starts.

You can then watch the intake port and see when it opens. When you get them both opening at the same time, you have maximised the available flow.

I've read that the 455 has a blowdown period of 12.5 degrees. That is not much time to get the pressure down in the cylinder. If you widen the exhaust, you can increase the port area during that blowdown cycle. The bigger opening will allow more exhaust gas to flow from the cylinder during that short blowdown. A generous muffler mod is also necessary with such a short blowdown cycle. A restrictive muffler will tend to keep the cylinder pressure higher during blowdown.


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## maggard (Apr 9, 2011)

I will chime in on the fuel usage. I have a 576 bought back in october. I use it to cut timber all day. The boss is a stihl man and he picked up a new 460 back in december. I can tell you there is no comparison in fuel usage. My 576 is at least 30% better on fuel. I can run it all day on around 6-7 tanks of fuel.


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## albert (Apr 9, 2011)

Yep those MS460's love mix. It's a factor for someone that put hours on a saw. I think hold more fuel than a 660 but don't run any longer between fill ups, maybe alittle less. LOL


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## Andyshine77 (Apr 10, 2011)

Terry Syd said:


> Brad, all these various stratos are a bit different and take a slightly different approach to each of them. As I said 'on my saw' I couldn't make the strato ports any bigger. This is a Husky 450 that is based upon the 445 - the engineers had trimmed every bit of port work they could to open it up. In fact, the strato butterfly was a big 16mm, but the manifold was only 13.5mm. It became clear why it was only 13.5mm after I calculated the area of the strato ports in the cylinder, that's all it needed.
> 
> However, the piston did partially block the ports in the cylinder, so I reworked the piston so that the whole system could flow like it was designed to. I even trimmed back the ends of the pin boss so that the air could get past it.
> 
> ...


 
Yes. More air in the cylinder/combustion chamber, means more fuel will be required this = more power.


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## MechanicMatt (Apr 16, 2011)

blsnelling said:


> I have ported quite a few strato saws, most of them with great success. I treat each model differently. The MS261 is one that I completel remove all strato clean air from. All of the air is charged with fuel. I tried it leaving the strato system intact, and it didn't respond like I wanted. Most other models I leave intact. This would include the little Ryobi/Redmax saw, which is the strongest 40cc class saw I've ever ported. The MS441 and MS362 also respond very well to porting and leaving the strato technology intact. The only saw I've had reliability issues with was the 372XP XT, and I removed it's strato stuff since it was designed VERY similiarly to the MS261. I've only done the one and did not try it leaving the strato still functional. The bottom line is that strato saw respond very well to porting. If the strato functionality is left functional, it can't help but save on fuel. One case that helps prove this, is that the MS261 H needle must be backed out 2 1/2 turns once I'm done with my mods. That's how much more fuel it needs to be rich enough. Fortunately, the carb still responds very well to adjustments at that point.


 
Brad what is the two covers on the side of the ryobi's cylinder for? And have any of your customers had any durability issues with there Ryobis that you know of? Just got one for free and want to learn all I can, Have been searching all over AS reading.


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## blsnelling (Apr 16, 2011)

MechanicMatt said:


> Brad what is the two covers on the side of the ryobi's cylinder for? And have any of your customers had any durability issues with there Ryobis that you know of? Just got one for free and want to learn all I can, Have been searching all over AS reading.


 
I only ported one, and that was a freebie for Eric Jeepers son's graduation present. Last I knew it was running great.


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## MechanicMatt (Apr 16, 2011)

blsnelling said:


> I only ported one, and that was a freebie for Eric Jeepers son's graduation present. Last I knew it was running great.


 
Did you mod the muffler first and run it then port it or port and muffler mod at the same time?? What Im trying to ask is how do you think it would respond to just a muffler mod?? I had a poulan strato saw that I opened up the muffler before I ever ran it so I had no way knowing if the muffler mod helped.


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## blsnelling (Apr 16, 2011)

MechanicMatt said:


> Did you mod the muffler first and run it then port it or port and muffler mod at the same time?? What Im trying to ask is how do you think it would respond to just a muffler mod?? I had a poulan strato saw that I opened up the muffler before I ever ran it so I had no way knowing if the muffler mod helped.


 
Honestly, I don't recall. I think I did a thread on it though.


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## promac850 (Apr 16, 2011)

MechanicMatt said:


> Did you mod the muffler first and run it then port it or port and muffler mod at the same time?? What Im trying to ask is how do you think it would respond to just a muffler mod?? I had a poulan strato saw that I opened up the muffler before I ever ran it so I had no way knowing if the muffler mod helped.


 
In general, all newer EPA saws love being muff modded, and ported too. Just a muff mod may be a huge improvement, and both would be awesome. 

I'm porting and muff modding the 350 Husky I recently am tripping over.  I expect it to be an easy to use, but fast cutting saw that is light enough for my dad to cut firewood with for a day or two. His back and shoulders are quite problematic for him and I want to reduce the chance of him being down for weeks with horrible pains.



blsnelling said:


> Honestly, I don't recall. I think I did a thread on it though.


 
Am I right that almost all newer EPA saws love being modded?


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## blsnelling (Apr 16, 2011)

promac610 said:


> Am I right that almost all newer EPA saws love being modded?


 
Almost *all *saws, period.


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## cheshire cat (May 31, 2011)

*Ryobi stratos*

being new to this I was taken with Brad's Ryobi and whilst not the most common model over here I found a 40cc "RCS4046C"-local designation. I have just started to find the faults (it was cheap)and now started stripping with a view to try a port job, do you have any timing figures from your job and does anyone ever alter the ignition timing on the tuned up jobs ? prob'ly enough questions for now :smile2:


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## maico490 (May 31, 2011)

This may be an over simplification but is it true to say that the air/fuel mixture flowing through the fuel butterfly of the carb on a strato saw is very rich and is then diluted by extra air from the strato port.


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## Andyshine77 (May 31, 2011)

maico490 said:


> This may be an over simplification but is it true to say that the air/fuel mixture flowing through the fuel butterfly of the carb on a strato saw is very rich and is then diluted by extra air from the strato port.


 
The opposite, you have less waste so less fuel is required.


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## cowboyvet (May 31, 2011)

Andyshine77 said:


> The opposite, you have less waste so less fuel is required.


 

I'm just trying to understand what your saying. More straight air through the strato port and LEANER air fuel mix through the transfer?

If my studies are correct the optimum air/fuel ratio (NOT oil mix ratio) is 12:1 for power. If you add straight air to the combustion chamber, wouldn't it require more fuel (say 9:1) through the transfers to get your combustion ratio back up to where it should be at 12:1? That is not saying it "drinks" more fuel, just burns it more efficiently because it keeps it in the chamber instead of the muffler and would have a higher fuel content down on the crankshaft possibly offering better lubrication qualities?

I'm just using air/fuel ratios for clarification purposes. I have never hooked a saw up to a 5 gas analyzer but that may be interesting to try just to see where they actually stand....


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## Andyshine77 (Jun 1, 2011)

cowboyvet said:


> I'm just trying to understand what your saying. More straight air through the strato port and LEANER air fuel mix through the transfer?
> 
> If my studies are correct the optimum air/fuel ratio (NOT oil mix ratio) is 12:1 for power. If you add straight air to the combustion chamber, wouldn't it require more fuel (say 9:1) through the transfers to get your combustion ratio back up to where it should be at 12:1? That is not saying it "drinks" more fuel, just burns it more efficiently because it keeps it in the chamber instead of the muffler and would have a higher fuel content down on the crankshaft possibly offering better lubrication qualities?
> 
> I'm just using air/fuel ratios for clarification purposes. I have never hooked a saw up to a 5 gas analyzer but that may be interesting to try just to see where they actually stand....


 
Your thinking there is more air in the combustion chamber, this is not so, as most of the pure air is escaping out of the exhaust port, in a conventional 2 cycle engine this would be unburnt air fuel mix, this is why they run dirty and less inefficient. Now there is some scavenging and mixing going on, but it's nominal IMHO, if you had to bump up the fuel mixture you would lose fuel efficiency. Now if you port the saw things change.:msp_smile: I really shouldn't have said it's the opposite I should have said the difference in jetting is nominal if any at all.


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## terry2tmd (Jun 1, 2011)

Great thread anyone got pictures of the piston mods to kinda help us more feeble minded?


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## Terry Syd (Jun 1, 2011)

The piston mods I made on my strato were straight forward. All I had to do was look through the strato port and see where the edges of the piston were restricting the flow. After I trimmed up those edges and got full flow through the ports, I then trimmed the ends of the pin bosses so that the air could flow more easily into the top of the transfer ports.

Each strato configuration is a bit different. So you would have take a look at the jug you have and how the piston fits relative to the ports.

You also need to take a look at the area of flow that is available to feed the strato function. Increasing the size of the strato ports in the jug won't do anything if the area of the butterfly feeding the existing ports is already too small for the area of the ports.

The most significant concept to grasp is that the 'gulp' (rate of demand) that the strato takes is determined by the width of the transfer ports. By that I mean that the strato function is always fully open when the butterfly is open and the piston cutaway is in position. The strato function (timing) doesn't begin to 'inhale' until the cutaway on the piston appears over the bottom of the transfer ports.

I did increase my 'gulp' factor a small amount by trimming the edge of the piston cutaway next to the transfer port. The cutaway had a curved top edge that partially blocked the transfer port as it was opening. I removed about .5mm from the corner of the curve to give it the maximum potential upon opening. - That mod is the equivalent of widening the intake port on a conventional two-stroke.

If all of this sounds like jibberish, then take a strato jug and piston, sit down with it and move the piston through its stroke. You will soon see how it all works and how to get the most flow from the strato function.


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## Terry Syd (Jun 1, 2011)

If it helps, here is an analogy. Think of the strato port as if it was an intake port on a conventional two-stroke.

The transfer port openings are like a conventional intake port opening. It is the entrance to the crankcase for the strato air.

The strato ports, piston cutaway and manifold are like the intake manifold on a conventional two-stroke.

The strato butterfly is like the carburetor.


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## cheshire cat (Jun 1, 2011)

Terry Syd said:


> If it helps, here is an analogy. Think of the strato port as if it was an intake port on a conventional two-stroke.
> 
> The transfer port openings are like a conventional intake port opening. It is the entrance to the crankcase for the strato air.
> 
> ...


 Terry --pics would be good (for us novices) I also thought your thoughts on piston skirt (intake) made good sense, also with all that piston cooling is there a case for more compression, and is there a case for modding the "stratos throttles"- i.e. relieving the "shear" effect on the leading edge of the actual holes (I've only seen the Ryobi version) cheers Nic


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## bluesportster02 (Jun 1, 2011)

great thread. opcorn:


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## Andyshine77 (Jun 1, 2011)

Strato animation,

<iframe width="480" height="390" src="http://www.youtube.com/embed/IY7zQKw4qsQ" frameborder="0" allowfullscreen></iframe>


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## Terry Syd (Jun 1, 2011)

Thanks Andy, if a picture is worth a thousand words, a video must be worth a million.

Since the piston skirt takes a direct blast of air, there are significant temperature gradients on the skirt. If you take a look at the above video you will see a scallop in the skirt above and forward of the strato cutaway on the skirt.

I expect that that scallop in the skirt is to help with an even expansion of the skirt. On my strato there is also a hole through the piston in the scallop. Since that scallop moves past the transfer port just prior to the strato cutaway, the hole allows the remaining mixture in the top of the transfer port to be drawn through the front part of the piston just behind the hot exhaust skirt.

I've seen several pictures of strato pistons, some have holes (of different sizes) and others do not. Since the pistons are all different, it appears the engineers did some emperical testing of what they needed to do to get a uniform expansion of the piston.


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## Andyshine77 (Jun 2, 2011)

Terry Syd said:


> Thanks Andy, if a picture is worth a thousand words, a video must be worth a million.
> 
> Since the piston skirt takes a direct blast of air, there are significant temperature gradients on the skirt. If you take a look at the above video you will see a scallop in the skirt above and forward of the strato cutaway on the skirt.
> 
> ...


 
I agree with you 100%. The first strato top end I had a chance to look at closely, I and others that were with me at the tame, came to may of the same conclusions. The piston temperatures must swing quit dramatically, one reason some of the early stratos were a bit coldblooded IMHO. I've also noted more carbon buildup in strato saws, I think this is also do to temperature changes.


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## Mastermind (Jan 14, 2012)

Digging up bones here....

The strato is the future, and the future is now.

I'm set on learning all that is to be had on these engines. :msp_sneaky:


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## Terry Syd (Jan 14, 2012)

Randy, there is this thread over in the '101' threads - http://www.arboristsite.com/saw-building-101/107976-14.htm

I gave the link to the last page as in the early pages I was trying to get my head around stratos and chainsaws - a lot of waffle and dead-end streets, but it could help someone from making the same mistakes I made.


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## Mastermind (Jan 14, 2012)

Terry Syd said:


> Randy, there is this thread over in the '101' threads - http://www.arboristsite.com/saw-building-101/107976-14.htm
> 
> I gave the link to the last page as in the early pages I was trying to get my head around stratos and chainsaws - a lot of waffle and dead-end streets, but it could help someone from making the same mistakes I made.



I've read everything that I can find on the strato and modded a few as well. I'm still attemting to understand the timing of the strato ports though. 

It seems to me that the strato ports need tho be timed a few degrees ahead of the intake ports to allow the fresh air charge to fill the transfers ahead of the incoming mixture. If they both open at the same time it seem like that would actually hamper flow?

A lot more to come on this subject is coming down the pipe.....

I'll be building a Husqvarna 562 in a few days.


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## mweba (Jan 14, 2012)

Mastermind said:


> I've read everything that I can find on the strato and modded a few as well. I'm still attemting to understand the timing of the strato ports though.
> 
> It seems to me that the strato ports need tho be timed a few degrees ahead of the intake ports to allow the fresh air charge to fill the transfers ahead of the incoming mixture. If they both open at the same time it seem like that would actually hamper flow?
> 
> ...



Yes, closer the timing equals less fresh air charge in the trans. Once the intake opens up the negative case pressure chooses the easiest path. 

I did have good results stuffing the upper trans with mix but that makes the whole strato design irrelevant.


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## Terry Syd (Jan 14, 2012)

"I'll be building a Husqvarna 562 in a few days." - Hot damn, now were going to see some interesting saw building. I hope you take heaps of pictures as you go.

I've been of different minds about staggering the strato and intake timing for different applications. There may be a small increase in fuel economy, emissions and low down lugging torque by having the strato timing open a few degrees before the intake.

The increase in low down lugging torque would be a result of having the 'back flow' through the intake at low revs begin in the strato port before the intake port. In other words, the there would be less tendancy for the mixture to become excessively rich at the low revs.

Having said that, I have still been able to lug the strato down quite well with the timing matched. It appears that the 'back flow' is split between both ports, so there is only half the back flow going up through the carb compared to a conventional engine. Basically, if you can build an engine with matched timing that will lug down lower in the rev range than you will ever practically use in the field, then there is no advantage to staggering the port timings.

The most obvious advantage of identical timings is being able to ensure that you are maximising the crankcase compression. The crankcase timing won't begin until both intake and strato timing are finished. If the strato timing finishes later, then that is when the base compression begins - and the contribution of the intake port has been 'short-changed' by finishing early.

I'm still in the 'matched timing' camp when it comes to the stratos.

For all out power, it would appear that compromising the strato port so that it flows fuel mixture would give an advantage. The fresh fuel mixture would tend to cool the upper ports and combustion chamber better than straight air and thus allow more charge density.

The compromised strato port may become a defining technique between a 'woods port' and a 'race port'.


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## 2stroked2smoke (Jan 14, 2012)

This is good info. I took the cylinder off my 562 tonight and am trying to wrap my mind around this configuration and what I'm gonna do. Here's some pics.


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## mweba (Jan 14, 2012)

The cylinder quality is superb is it not


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## 2stroked2smoke (Jan 14, 2012)

top notch. looks like the strato ports open way before the intake. See what you think.


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## parrisw (Jan 14, 2012)

mweba said:


> The cylinder quality is superb is it not



Ya it looks real nice!


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## Terry Syd (Jan 14, 2012)

Here's some other pictures you need with the jug on the saw.

Take one of the transfer covers off and take a picture of the strato cutaway just peeking over the bottom of the transfer port. You want to check that the opening is completely flat (no curvature from the cutaway). This will give you the fastest opening of the strato port.

Take another picture from the back of the jug (no manifold) with the piston at TDC. You want to check that the piston does not block any of the flow in the strato ports.

Check the timing of the strato port with the transfer cover off, then compare it to the intake timing. You'll probably find there is about 10 degrees difference.


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## Terry Syd (Jan 14, 2012)

"looks like the strato ports open way before the intake." - nope.

This has been a common misconception with guys starting out to mod stratos, they use old habits and look at the back of the jug for the timing figures. The strato port opens at the transfer port.

The openings at the back of the jug must be open BEFORE the transfer port opens so that the transfer port openings have an open conduit to work with. If the back ports opened at the same time, it would just create more restriction, so the back ports are opened first to get ready for the transfer port opening.


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## mweba (Jan 14, 2012)

2stroked2smoke said:


> top notch. looks like the strato ports open way before the intake. See what you think.



Yes. When studying my 555 cylinder, I was trying to figure a way to reduce the advance on the strato ports. In turn loading less clean air in to the transfers. Lost interest and never sorted it out......


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## tree monkey (Jan 14, 2012)

can you give us the stock timing numbers ? thanks


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## mweba (Jan 14, 2012)

Terry Syd said:


> "looks like the strato ports open way before the intake." - nope.
> 
> This has been a common misconception with guys starting out to mod stratos, they use old habits and look at the back of the jug for the timing figures. The strato port opens at the transfer port.
> 
> The openings at the back of the jug must be open BEFORE the transfer port opens so that the transfer port openings have an open conduit to work.



I don't remember this being the case but could have completely over looked it on this configuration. Interesting


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## mweba (Jan 14, 2012)

tree monkey said:


> can you give us the stock timing numbers ? thanks



I believe they are earlier in this thread, Scott. Will check


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## blsnelling (Jan 14, 2012)

I don't find them so different to port than a non-strato saw.


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## Chris-PA (Jan 14, 2012)

Cool pictures, neat parts. The engineer in me really likes these strato designs. Just puking raw fuel out the exhaust port is gross, this is a much more elegant solution. There is more complexity, but that complexity is mostly in the design - it manifests in the shape of the ports and the piston, plus and extra butterfly. The finished design is not that mechanically complicated with lots of fussy moving parts, and the basic function remains the same. It's just filling the end of the transfer runner with air before charging the cylinder, so that air is the first thing pumped in. There's no reason they couldn't have made this stuff a long time ago.


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## 2stroked2smoke (Jan 14, 2012)

Terry Syd said:


> "looks like the strato ports open way before the intake." - nope.
> 
> This has been a common misconception with guys starting out to mod stratos, they use old habits and look at the back of the jug for the timing figures. The strato port opens at the transfer port.
> 
> The openings at the back of the jug must be open BEFORE the transfer port opens so that the transfer port openings have an open conduit to work with. If the back ports opened at the same time, it would just create more restriction, so the back ports are opened first to get ready for the transfer port opening.



OK, I see what your saying now. Looks like the strato is opening into the transfer port about 4 degrees after the intake opens. This is a pic of the piston with some tape on it to mark how much I would have to remove to make the timing on both ports open at the same time.


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## Mastermind (Jan 14, 2012)

2stroked2smoke said:


> OK, I see what your saying now. Looks like the strato is opening into the transfer port about 4 degrees after the intake opens. This is a pic of the piston with some tape on it to mark how much I would have to remove to make the timing on both ports open at the same time.



You said the strato ports open after the intake ports. Interesting. I would have thought the stratos would have open slightly ahead....

This is a great discussion. I really expect to see more and more of these so we MUST learn everything we can about them and share it freely.


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## 2stroked2smoke (Jan 15, 2012)

Well I went ahead and changed the strato port timing to match the intake timing. I also took the exhaust port width from 58% of cylinder width to 65% of cylinder width. Started it up and it runs pretty good. I'm gonna go cut some firewood tommorrow. I'll let ya know how it runs.


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## Terry Syd (Jan 15, 2012)

Yeah, I was also expecting the strato timing to be more advanced/longer than the intake timing.

I notice that the cutaway on the piston has been smoothed from the factory. It is already shaped for good flow, whereas the first stratos had pin bosses sticking out and disrupting the flow.

EDIT: I'm wondering if you matched the intake of the STRATO port rather than the intake of the intake port where the CARBURETOR is located.


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## 2stroked2smoke (Jan 15, 2012)

I matched the strato port on the piston opening up to the transferport with the bottom of the piston opening up the intake port. That's the way I was understanding you. Did I misunderstand you?


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## mweba (Jan 15, 2012)

2stroked2smoke said:


> I matched the strato port on the piston opening up to the transferport with the bottom of the piston opening up the intake port. That's the way I was understanding you. Did I misunderstand you?



That is the way I understood his explanation as well. This is why I was confused about the port opening after the intake. The stratos I've dealt with, the strato port opens a couple degrees before the intake, causing negative pressure to draw fresh into the upper trans. If the timing is matched,with the intake, less fresh is drawn into the uppers for the incoming charge.


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## mweba (Jan 15, 2012)

The only way I could figure to do this would be to lift the piston skirt or lower the intake....loosing crank case pressure. Not sure less pressure is bad but it is more expensive to correct later.


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## 2stroked2smoke (Jan 15, 2012)

This is the first strato saw that I've ported. It is a little confusing but I'm starting to understand how it works. Have you timed your ports to see when they open MWEBA? I'm just curious if your findings match mine. My intake was opening 3-4 degrees before the strato port.


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## mweba (Jan 15, 2012)

2stroked2smoke said:


> This is the first strato saw that I've ported. It is a little confusing but I'm starting to understand how it works. Have you timed your ports to see when they open MWEBA? I'm just curious if your findings match mine. My intake was opening 3-4 degrees before the strato port.



Not in the following pics it isn't. Is the side piston port not open to the upper transfers at this point? I have not degreed mine or the 555 I owned. Never had the time or interest in porting one.



2stroked2smoke said:


> top notch. looks like the strato ports open way before the intake. See what you think.


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## 2stroked2smoke (Jan 15, 2012)

mweba said:


> The only way I could figure to do this would be to lift the piston skirt or lower the intake....loosing crank case pressure. Not sure less pressure is bad but it is more expensive to correct later.



The crankcase on my 562 is the tightest I've ever seen. The clearances between the crankshaft and crankcase were very tight. It even had a plastic stuffer between the crank and connecting rod. Just enough room for the rod to cear and that's it. This has to build some good crankcase pressures.


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## Mastermind (Jan 15, 2012)

My mind is at work on the 562 as we speak. BUT I have three saws ahead of it and two of those are 7900s and I have a lot of learning on those beasts as well to do. They are pretty straight forward though.......lots of blowdown and gobs of compression. 


These strato saws are coming clearer in terms of port work though. I seems that by altering the timing of the strato ports one could change the characteristics of the engine, and that is just one variable.

I'm thinking that by increasing intake and strato timing plus evening the two that could serve to fill the case. Then raising the exhaust port and transfer inlets together should raise the working rpm just like any other saw. 

Has anyone done much on compression increase in a strato?


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## mweba (Jan 15, 2012)

Mastermind said:


> My mind is at work on the 562 as we speak. BUT I have three saws ahead of it and two of those are 7900s and I have a lot of learning on those beasts as well to do. They are pretty straight forward though.......lots of blowdown and gobs of compression.
> 
> 
> These strato saws are coming clearer in terms of port work though. I seems that by altering the timing of the strato ports one could change the characteristics of the engine, and that is just one variable.
> ...



All in all they are the same as any 2 stroke. Just searching for the most efficient charge per compression. The strongest 372XT I built was at 187psi.


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## 2stroked2smoke (Jan 15, 2012)

mweba said:


> Not in the following pics it isn't. Is the side piston port not open to the upper transfers at this point? I have not degreed mine or the 555 I owned. Never had the time or interest in porting one.



The strato ports on the intake side of the jug open way before the intake does, but the strato ports on the piston don't open up into the transfers until about 3-4 degrees after the intake port starts to open. The strato ports on the piston is what I changed to make the timing match. I just raised the port onthe piston until it opened into the transferports at the same time as the intake opened.


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## mweba (Jan 15, 2012)

2stroked2smoke said:


> The strato ports on the intake side of the jug open way before the intake does, but the strato ports on the piston don't open up into the transfers until about 3-4 degrees after the intake port starts to open. The strato ports on the piston is what I changed to make the timing match. I just raised the port onthe piston until it opened into the transferports at the same time as the intake opened.



Got ya. This is different than the 372xt. Basically, you are adding more fresh air duration to your stroke cycle. Some kind of a running change must have take place? Easier to recast a new piston than a cylinder?


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## Terry Syd (Jan 15, 2012)

2stroked2smoke said:


> I matched the strato port on the piston opening up to the transferport with the bottom of the piston opening up the intake port. That's the way I was understanding you. Did I misunderstand you?



Nope, that is what I was referring to. It looks like this 562 is the first strato we've worked on where the strato timing was less than the intake timing.


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## Terry Syd (Jan 15, 2012)

mweba said:


> The only way I could figure to do this would be to lift the piston skirt or lower the intake....loosing crank case pressure. Not sure less pressure is bad but it is more expensive to correct later.



When you match the two timings, you don't loose any base compression. The base compression can only start when the last port closes, which ever port it is. By matching them you retain the same compression, but increase the potential flow into the crankcase.

I'm a fan of cutting the piston as they can easily be replaced.


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## Terry Syd (Jan 15, 2012)

Mastermind said:


> These strato saws are coming clearer in terms of port work though. I seems that by altering the timing of the strato ports one could change the characteristics of the engine, and that is just one variable.
> 
> I'm thinking that by increasing intake and strato timing plus evening the two that could serve to fill the case. Then raising the exhaust port and transfer inlets together should raise the working rpm just like any other saw.
> 
> Has anyone done much on compression increase in a strato?



You got it. Once you have the ports matched, then if you need more 'intake' timing, then both intake and strato ports are moved together.

These Husky stratos are famous for having very low blowdown figures - around 12 degrees. As I recall this 562 was measured at 11 degrees. It doesn't take much of an increase to create a significant difference to the blowdown. If you raised the blowdown just 2 degrees to 13 degrees, that is a *18%* increase in the time for blowdown. Add in the extra area by widening the port and you have a big increase in blowdown.

I took the cautious route and trimmed a couple of degrees off the front of the piston (about .5mm off the edge - again pistons are cheaper than jugs). The change to the engine speed was impressive. I went back in and cut another 2 degrees on the piston for a total of 16 degrees of blowdown, but the engine didn't need it. I then went back and cut the jug for 14 degrees and put in a fresh piston.


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## 2stroked2smoke (Jan 15, 2012)

Went out with the 562 today, and downed about 30 elms. Cut up three of them into firewood. I'm impressed with my saw with the new cylinder mods. It actually felt smoother. It started out cutting a little hyper but the autotune brought it back down after a little cutting. This is one thing that I don't understand about porting an autotune. The autotune works at adjusting the carb based on engine rpm. So if you do cylinder mods to raise the working rpm, won't the autotune adjust the carb to bring it back down. I can see getting more torque but don't see you being able to raise the working rpm.


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## tree monkey (Jan 15, 2012)

2stroked2smoke said:


> Went out with the 562 today, and downed about 30 elms. Cut up three of them into firewood. I'm impressed with my saw with the new cylinder mods. It actually felt smoother. It started out cutting a little hyper but the autotune brought it back down after a little cutting. This is one thing that I don't understand about porting an autotune. The autotune works at adjusting the carb based on engine rpm. So if you do cylinder mods to raise the working rpm, won't the autotune adjust the carb to bring it back down. I can see getting more torque but don't see you being able to raise the working rpm.



i was thinking the same thing


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## parrisw (Jan 15, 2012)

There has to be something else the fuel curve is based upon besides just RPM. It just wont work well with 1 input, even just two inputs is very crude compared to Automotive standards.


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## Terry Syd (Jan 15, 2012)

When you increased the duration of the strato port, you increased the amount of air going to the cylinder. In other words, the saw started out initially a bit lean, or as you said 'hyper'. The autotune eventually worked out the change and set the mixture.

The autotune works to set the mixture, it doesn't work on the rpm. It does this by changing the mixture and recognizing any change in rpm. If it leans it out and the rpm goes up, then it needs to change the baseline mixture to run a bit leaner. If it leans it out and the rpm goes down, then it needs to change the baseline mixture to run a bit richer. The autotune is looking for an optimum fuel mixture at a given load.

EDIT: If you want to see an increase in cutting speed, try adding just two degrees of blowdown. You can nip the front of the piston to get that extra blowdown. The amount of loss in compression from the removed material is minimal and you probably wouldn't notice it - especially if you are increasing the ability of the engine to charge the cylinder.

If you don't like the change, then it is simple to put a stock piston back in.


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## tree monkey (Jan 15, 2012)

Terry Syd said:


> When you increased the duration of the strato port, you increased the amount of air going to the cylinder. In other words, the saw started out initially a bit lean, or as you said 'hyper'. The autotune eventually worked out the change and set the mixture.
> 
> The autotune works to set the mixture, it doesn't work on the rpm. It does this by changing the mixture and recognizing any change in rpm. If it leans it out and the rpm goes up, then it needs to change the baseline mixture to run a bit leaner. If it leans it out and the rpm goes down, then it needs to change the baseline mixture to run a bit richer. The autotune is looking for an optimum fuel mixture at a given load.



are you saying that if you can feed it enough air/ fuel it will turn, lets say, 20,000 rpm? or is it rev limited? will it be way rich?


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## Terry Syd (Jan 15, 2012)

Naw, all engines have their limits. For example, you can put a limit on a saw's working rpm by limiting the blowdown - the saw will eventually hit a point where there is so much blowback down the transfers that it can't rev any higher.

After going through Blair's work it appears that most, if not all, new saws are being set up with a shorter exhaust duration in order to decrease emissions. In the case of these Husky stratos the stock blowdown is very low compared to other saws. I found that a two degree increase on my Husky strato (from 12 degrees of blowdown to 14) really woke it up.

I don't know if the 562 is limited, but I would expect that it is. An increase in cutting speed will probably still be well within that limited coil.

The autotune appears to be rather simple. It will change the mixture and then note whether the rpm went up or down. It does that whether you are dogging in at 7,000 rpm or cutting at 10,000 - it will probably continue to do that function right up until it hits the limiter.


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## tree monkey (Jan 15, 2012)

Terry Syd said:


> Naw, all engines have their limits. For example, you can put a limit on a saw's working rpm by limiting the blowdown - the saw will eventually hit a point where there is so much blowback down the transfers that it can't rev any higher.
> 
> After going through Blair's work it appears that most, if not all, new saws are being set up with a shorter exhaust duration in order to decrease emissions. In the case of these Husky stratos the stock blowdown is very low compared to other saws. I found that a two degree increase on my Husky strato (from 12 degrees of blowdown to 14) really woke it up.
> 
> ...



i guess what i'm asking is will the auto tune work at 20,000?


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## 2stroked2smoke (Jan 15, 2012)

Terry Syd said:


> When you increased the duration of the strato port, you increased the amount of air going to the cylinder. In other words, the saw started out initially a bit lean, or as you said 'hyper'. The autotune eventually worked out the change and set the mixture.
> 
> The autotune works to set the mixture, it doesn't work on the rpm. It does this by changing the mixture and recognizing any change in rpm. If it leans it out and the rpm goes up, then it needs to change the baseline mixture to run a bit leaner. If it leans it out and the rpm goes down, then it needs to change the baseline mixture to run a bit richer. The autotune is looking for an optimum fuel mixture at a given load.
> 
> ...



That makes sense. So you think if I increase my blowdown by 2 or 3 degrees that it will wake it up. I'll give it a try.


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## mdavlee (Jan 15, 2012)

The 555 has the same exhaust and transfer numbers as the 562. I want to say it was 12° of blowdown. The 576 was 102° exhaust, 13° of blowdown and 74° intake. Just raising the exhaust 2° seemed to make a huge difference. I lowered the intake 4° and left the strato ports alone. I don't remember the timing number on them off the top of my head. It seems to cut with a lot more rpms in the cut and sounds pretty much the same out of the cut.


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## Terry Syd (Jan 15, 2012)

I'm old school. I prefer to cut the piston and see where the 'sweet spot' is. You can try 13 degrees, then 15 degrees, etc. At some point you are going backward. Now you know where the sweet spot is and you can cut the jug to that duration. 

I expect with just two degrees you will be surprised. If it is just two degrees, then for most people it won't be worth cutting the jug, just nip the crown at the exhaust port and run it. The factory cylinder liner isn't compromised and you can still go back to stock if you want it.


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## Stihlman441 (Jan 15, 2012)

Terry Syd said:


> Brad, all these various stratos are a bit different and take a slightly different approach to each of them. As I said 'on my saw' I couldn't make the strato ports any bigger. This is a Husky 450 that is based upon the 445 - the engineers had trimmed every bit of port work they could to open it up. In fact, the strato butterfly was a big 16mm, but the manifold was only 13.5mm. It became clear why it was only 13.5mm after I calculated the area of the strato ports in the cylinder, that's all it needed.
> 
> However, the piston did partially block the ports in the cylinder, so I reworked the piston so that the whole system could flow like it was designed to. I even trimmed back the ends of the pin boss so that the air could get past it.
> 
> ...



With the richen the mixture and get more fuel into the saw what about the MTronic and Auto tune saws ?,has anyone worked out how to adjust the electronics to acheave this ?.


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## Mastermind (Jan 15, 2012)

Terry Syd said:


> You got it. Once you have the ports matched, then if you need more 'intake' timing, then both intake and strato ports are moved together.
> 
> These Husky stratos are famous for having very low blowdown figures - around 12 degrees. As I recall this 562 was measured at 11 degrees. It doesn't take much of an increase to create a significant difference to the blowdown. If you raised the blowdown just 2 degrees to 13 degrees, that is a *18%* increase in the time for blowdown. Add in the extra area by widening the port and you have a big increase in blowdown.
> 
> I took the cautious route and *trimmed a couple of degrees off the front of the piston* (about .5mm off the edge - again pistons are cheaper than jugs). The change to the engine speed was impressive. I went back in and cut another 2 degrees on the piston for a total of 16 degrees of blowdown, but the engine didn't need it. I then went back and cut the jug for 14 degrees and put in a fresh piston.



So you are saying you in effect raised the exhaust port two degrees and left the transfers as is.

Did you ever try raising the transfer ports?


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## 2stroked2smoke (Jan 15, 2012)

Mastermind said:


> So you are saying you in effect raised the exhaust port two degrees and left the transfers as is.
> 
> Did you ever try raising the transfer ports?



Wouldn't that be going backwards and decreasing blowdown?


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## Terry Syd (Jan 15, 2012)

Randy, my 450 was an odd ball saw to start working on. It is based on the 445 (45cc). When I checked the area of the transfer ports I saw that they were already 9% too small for the ports on the 50cc 450.

However, it got worse - I needed more transfer area, so I increased the width of the ports by another 12.5%. Add the 9% deficit to the 12.5% increase and I had to make the transfer tunnels another 21.5% larger - now that took some effort to get it all to flow correctly. I ended up grinding out the back of the transfer tunnel covers and building them up with fiberglass and GB weld. 

I ended up with .0066 m/sec at 10,500rpm on the transfers, which works great. 

Not a project for the faint of heart, but at 10.8lb, NK bar and 8 pin, it will stay with my mate's 365 in big Aussie hardwood. In fact, I have to get a re-match with him as I think that the last few changes may give me the edge.

Going back to the 562, if the revs are increased significantly by the additional blowdown, then there may be the need to widen the ports. I say widen rather than raising as the transfer tunnels may be easier to widen than to raise them. It will also prevent chasing more exhaust timing to keep the blowdown figures.

These Husky stratos have a lot of potential with the strato function, they can flat suck some air. I am running a 570 carb on my 450. The combined area of the strato function and 570 carb is equivalent to a 19mm carb. I expect that the 562 has a 12-12.5mm venturi in the carb. Since it is the same C1M carb as the 570, then someone will probably eventually slip on the larger 13.5mm 570 carb on the 562.


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## parrisw (Jan 15, 2012)

Mastermind said:


> So you are saying you in effect raised the exhaust port two degrees and left the transfers as is.
> 
> Did you ever try raising the transfer ports?



Ya, I'm kinda confused as well Randy??? I've never heard anyone say they just increased blowdown? To do that you need more spacing between the transfers and the ex, the only way to do that is raise the ex. Or lower the jug then raise the ex that amount, so ex would be unchanged, blowdown would increase, but intake would increase as well.


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## Terry Syd (Jan 15, 2012)

You guys are focusing on timing. Remember it is time/area of the ports that really matters. That's why it helps to widen the exhaust port, you are increasing the area of the port during blowdown.

The 562 transfer tunnels look a lot easier to modify than the homeowner 450. If the 562 needs more transfer time/area I expect that you will find it easy to accomplish by making the transfer ports wider.


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## Mastermind (Jan 15, 2012)

2stroked2smoke said:


> Wouldn't that be going backwards and decreasing blowdown?




If you raised the exhaust 4° and the transfers 2° you would net a 2° increase in blowdown. I just was wondering if raising the transfers would increase working rpm. There's more to the equation than blowdown. 



Terry Syd said:


> Randy, my 450 was an odd ball saw to start working on. It is based on the 445 (45cc). When I checked the area of the transfer ports I saw that they were already 9% too small for the ports on the 50cc 450.
> 
> However, it got worse - I needed more transfer area, so I increased the width of the ports by another 12.5%. Add the 9% deficit to the 12.5% increase and I had to make the transfer tunnels another 21.5% larger - now that took some effort to get it all to flow correctly. I ended up grinding out the back of the transfer tunnel covers and building them up with fiberglass and GB weld.
> 
> ...



I remember that build very well Terry. I did a 450 shortly after and your build helped immensely. 



parrisw said:


> Ya, I'm kinda confused as well Randy??? I've never heard anyone say they just increased blowdown? To do that you need more spacing between the transfers and the ex, the only way to do that is raise the ex. Or lower the jug then raise the ex that amount, so ex would be unchanged, blowdown would increase, but intake would increase as well.



You could raise just the exhaust and increase blowdown. I've been trying to maintain factory blowdown on most saws by raising both exhaust and transfers together. On some newer saws that doesn't work well though.

I've found that raising the transfers on some saws really helps them hold a higher rpm in the cut. I just wonder if the same would be true on these strato saws?


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## Terry Syd (Jan 15, 2012)

Randy, I can tell you that when I finally got those transfers opened up on the 450 it held its rpm in the cut very well.

We still have not seen a picture of the side of the 562 jug with the transfer covers off. A picture of the inside of the transfer covers would also be informative. The ones on the 450 had some flow inserts that were relatively easy to modify in order to widen the ports - it was getting the rest of the tunnel to flow that port that was the real challenge, but the 562 looks easy.


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## Mastermind (Jan 15, 2012)

Terry Syd said:


> Randy, I can tell you that when I finally got those transfers opened up on the 450 it held its rpm in the cut very well.
> 
> We still have not seen a picture of the side of the 562 jug with the transfer covers off. A picture of the inside of the transfer covers would also be informative. The ones on the 450 had some flow inserts that were relatively easy to modify in order to widen the ports - it was getting the rest of the tunnel to flow that port that was the real challenge, but the 562 looks easy.



I'll be starting a thread on this saw in a few days with lots of pictures.

I have several woods ports ahead of it, but I will get a stock video and pictures to study asap.


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## w8ye (Jan 15, 2012)

What about these?


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## Terry Syd (Jan 16, 2012)

If it needs more transfer area, then those ports will be a piece of cake to work on and widen. There's plenty of meat in the transfer covers to increase the area if need be.

Take a look at the second picture of the inside of the transfer cover. You can see all the soot from the blowback into the transfers. The covers on my 450 had the soot going halfway down into the crankcase. I expect with the crankstuffers on the 562 that the extra base compression may help to prevent some of the blowback, but in any case the added compression will help the transfer flow to make up for lost time.

The blowback into the transfers was one of the unusual things I found on the Husky stratos. I expect the long transfer tunnels are designed to contain the blowback and then use it to help purge the cylinder.

Once the transfer flow reverses, the blowback gases enter the cylinder first where they collide and mix with the exhaust gases that are in the cylinder. It doesn't matter if those gases get mixed together, it is just exhaust mixing with exhaust. Then as the flow gets established in the cylinder, the fresh air from the strato follows the train of gases up the back of the cylinder, followed by the rich mixture from the carb.

The result is less mixing of air/fuel mixture with the remaining exhaust gases in the cylinder. 

Further, the relatively long transfer duration and late closing of the transfers allows a better trapping efficiency of the intake charge just before the exhaust closes.

The whole design is different from what we are used to, but when you think about it, it sure is clever.


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## tree monkey (Jan 16, 2012)

all that black in the transfer tells me that there is not enough blow down


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## parrisw (Jan 16, 2012)

tree monkey said:


> all that black in the transfer tells me that there is not enough blow down



Does that mean its getting some reverse flow? Ex going down the transfers.


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## parrisw (Jan 16, 2012)

Maybe I'm not getting this totally but blowdown to me is the time between the ex opening and the transfers opening. So how does giving the transfers more area increase this time? My thinking it cant. If you widen the area of the transfers, you're getting more flow, but is it really more time? I keep hearing time/area?


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## tree monkey (Jan 16, 2012)

parrisw said:


> Does that mean its getting some reverse flow? Ex going down the transfers.



yes


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## Terry Syd (Jan 16, 2012)

Yep, that's what the black soot is, blowback. On a conventional two-stroke you may only find that around the transfer ports, but the Husky stratos it gets way down the tunnels.

However, here's the point to remember - how much blowdown is enough? The answer is easy - "enough".

You can find that out by taking a bit off the front of the front of the piston to increase the blowdown. You keep going until you go past the 'sweet spot'. Now you know how much is 'enough'.


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## parrisw (Jan 16, 2012)

tree monkey said:


> yes



Thanks. Tis what I thought.


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## Terry Syd (Jan 16, 2012)

Will, Google 'time/area two-stroke' and you should find lots of references to time/area for porting. If you can pull up a copy of Jennings 'Two-stroke Tuners Handbook' he has a good discussion on it. 

It is an old 'rule of thumb' of tuners to go for area before going for timing.


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## tree monkey (Jan 16, 2012)

parrisw said:


> Maybe I'm not getting this totally but blowdown to me is the time between the ex opening and the transfers opening. So how does giving the transfers more area increase this time? My thinking it cant. If you widen the area of the transfers, you're getting more flow, but is it really more time? I keep hearing time/area?



you need to do some reading on port time area and port mean time, jennings is good for this. it's hard to exlplain.
macking the ex port wider gives the port more time area so the ex gas gots out faster. so you don't need as mutch blow down. 
does that help?


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## tree monkey (Jan 16, 2012)

terry beat me to it


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## parrisw (Jan 16, 2012)

tree monkey said:


> you need to do some reading on port time area and port mean time, jennings is good for this. it's hard to exlplain.
> macking the ex port wider gives the port more time area so the ex gas gots out faster. so you don't need as mutch blow down.
> does that help?



Yes, thanks, that makes sense, I guess I did know that. I'm just thinking out loud here. It helps me to understand things to just talk about it. Sometimes hard to think about it.


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## 2stroked2smoke (Jan 17, 2012)

Here's a video of my 562 that I've matched the strato and intake timing, opened exhaust to 65% and raised the exhaust port 2-3 degrees. It runs pretty good. I was planning on cutting firewood today but it flippin freezing out. I was planning on cutting up a bunch of bigger wood to really let the autotune settle in but I ended up just making about 10 cuts in a 12 inch log to set it before I made the video. Good chance the saw will run better with some more run time.


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## mweba (Jan 17, 2012)

So...What do you think? Impossible to tell from the video but the revs don't "sound" any higher. Not being critical, just trying to decide if mine remains stock


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## 2stroked2smoke (Jan 17, 2012)

mweba said:


> So...What do you think? Impossible to tell from the video but the revs don't "sound" any higher. Not being critical, just trying to decide if mine remains stock



I'm not overly impressed yet. It kinda feels like I might of lost a little bit of torque. Like I said though, I haven't run it enough to really let the autotune settle in. It COLD out there. That wind is vicious. I keep ya updated as I cut more with it. I have a new 562xp coming next month. When I get that one I can compare them side by side.


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## blsnelling (Jan 17, 2012)

Doesn't sound like the RPMs are there yet. What did you do with the transfers? Sorry if I missed it.


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## 2stroked2smoke (Jan 17, 2012)

blsnelling said:


> Doesn't sound like the RPMs are there yet. What did you do with the transfers? Sorry if I missed it.



I didn't do anything to the transfers. I just raised the exhaust port 2-3 degrees to increase my blowdown to 14 degrees. I matched the intake and strato port opening timing and I widened the exhaust to 65%.


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## weimedog (Jan 17, 2012)

Seems to me the RPM's in his video are defined by how hard he's pushing in the cut, the question for me would be a before and after time in the cut. (Different pressures at equal chain speeds might realize different chip size therefore cut time is the base assumption. ) So really can't tell much from the vid..at least I can't:msp_sad:


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## 2stroked2smoke (Jan 17, 2012)

OK, wasn't happy with the saw losing torque. The changes that I made shouldn't have made that much difference torque wise. Got to wondering if the engine was using more fuel now and maybe the carb was maxxed out on adjustment on the auto tune. I dissassembled the carb and raised the lever that operates the needle and seat so more fuel was available. Bingo! The saw revs and cuts better than it ever has. Makes me think that this setting was off from the beginning. I had a hesitation on acceleration when this saw was new. Upon terry's advice I shortened the spring under the lever. This helped but was probably just masking the real problem. Nobody else seams to have had this problem so hopefully this was just a fluke.


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## mweba (Jan 17, 2012)

Did you check squish? Seem to remember the triple five being closer to a smoosh


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## 2stroked2smoke (Jan 17, 2012)

No. I had no intentions of changing the squish so I never measured it.


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## blsnelling (Jan 17, 2012)

2stroked2smoke said:


> No. I had no intentions of changing the squish so I never measured it.



Why not? You're missing a big piece of the puzzle not changing the transfers. Did you alter the strato ports?


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## Andyshine77 (Jan 17, 2012)

Setting the squish can make a pretty big difference. Sounds like the pop off pressure was too high and the lever was too low, AKA normal for a new saws these days.


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## funky sawman (Jan 17, 2012)

2stroked2smoke said:


> OK, wasn't happy with the saw losing torque. The changes that I made shouldn't have made that much difference torque wise. Got to wondering if the engine was using more fuel now and maybe the carb was maxxed out on adjustment on the auto tune. I dissassembled the carb and raised the lever that operates the needle and seat so more fuel was available. Bingo! The saw revs and cuts better than it ever has. Makes me think that this setting was off from the beginning. I had a hesitation on acceleration when this saw was new. Upon terry's advice I shortened the spring under the lever. This helped but was probably just masking the real problem. Nobody else seams to have had this problem so hopefully this was just a fluke.



How much did you raise the inlet needle lever?


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## 2stroked2smoke (Jan 17, 2012)

funky sawman said:


> How much did you raise the inlet needle lever?



About .015 It doesn't take much to make a big difference


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## funky sawman (Jan 17, 2012)

WOW:msp_ohmy: .015" that is alot, I dont normally move them more than .005, but if that worked for you and your idle is stable in any position, COOL


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## Terry Syd (Jan 17, 2012)

Good catch on the metering lever height. When you get the new stock 562 it would be interesting to see if it is set low. Obviously your mods took the demand to the stock set-up carb past the point that it was capable of tuning for - that's a good sign. 

It will be interesting to see the comparison of your modded 562 with the stocker.

EDIT: I just remembered that when I bored out the stock carb on the 450 that it wouldn't flow enough fuel. I checked the metering lever height and instead of being level with the carb body it was down below it. I had to raise the lever up about .5mm or .020". That fixed the problem. I'm wondering if the metering lever height should be checked on all these Husky stratos.


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