Wanna Talk About Port Shapes?

[Brush Ape]

I'm not the only one.

Imagine no compression
It's easy if you try
No saw performance
Without no PSI
Imagine all the people
Freezing all today...

Imagine there's no firewood
It isn't hard to do
Nothing in your pickup
Or in your woodpile, too
Imagine all the people
Paying for LP...

You may say my saw's a screamer
But I'm not the only one
When Randy made my saw
One runnin' son of a gun

Imagine two stroke obsession
I wonder if you can
No more crappy wildthing
Only three saw plan
Imagine all the people
Splitting all that wood...

You may say my saw's a screamer
But I'm not the only one
I hope someday you'll join us
Piss revving so much fun

 

[dl5205]

Imagine no compression
It's easy if you try
No saw performance
Without no PSI
Imagine all the people
Freezing all today...

Imagine there's no firewood
It isn't hard to do
Nothing in your pickup
Or in your woodpile, too
Imagine all the people
Paying for LP...

You may say my saw's a screamer
But I'm not the only one
When Randy made my saw
One runnin' son of a gun

Imagine two stroke obsession
I wonder if you can
No more crappy wildthing
Only three saw plan
Imagine all the people
Splitting all that wood...

You may say my saw's a screamer
But I'm not the only one
I hope someday you'll join us
Piss revving so much fun

 

[Deets066]

Imagine no compression
It's easy if you try
No saw performance
Without no PSI
Imagine all the people
Freezing all today...

Imagine there's no firewood
It isn't hard to do
Nothing in your pickup
Or in your woodpile, too
Imagine all the people
Paying for LP...

You may say my saw's a screamer
But I'm not the only one
When Randy made my saw
One runnin' son of a gun

Imagine two stroke obsession
I wonder if you can
No more crappy wildthing
Only three saw plan
Imagine all the people
Splitting all that wood...

You may say my saw's a screamer
But I'm not the only one
I hope someday you'll join us
Piss revving so much fun

You been drinking?

 

[Mastermind]

Who are y'all talking to?

 

[Duane(Pa)]

Who are y'all talking to?

John Lennon showed up and sang us a song.

 

[Adirondackstihl]

Here's what great guys hang out on these sites.

I mentioned needing an 064 jug. Three arrived in a few days.

Should I mention I need a 268 carb?

 

[Terry Syd]

Taking a look at DC's jug again, maybe he wasn't trying to correct the flow of the rear 'boost ports' with the addition of the grooves below the transfer ports. I've seen jugs ported like that without the rear groove 'boost ports'.

Perhaps the grooves below the transfer ports are used to alter the flow into the cylinder - like a 4-port Husky might use on a 372. On the 372 the ports closest to the intake are angled up a bit. Of course, the up-angle decreases time/area a bit, but if the up-angle creates a better flow in the loop scavenging then it can be a boost in power.

Back to DC's cylinder - The lower grooves below the transfer port create a situation like on an open-port cylinder. That is, the flow attached to the side of the piston 'lifts' the flow off of the top of the piston and angles it higher in the cylinder. What you would then have with the single port cylinder would be the part of the flow closest to the exhaust port angling across the piston while the part closest to the intake port taking a steeper angle up into the combustion chamber (just like the 372 4-port). The good thing about such a mod would be that you would not reduce the time/area of the port by changing the internal dimensions, you would simply be tweaking the flow as it entered the cylinder.

 

[Mastermind]

Terry that's what I see with the bridge ports too.....more of a change in flow direction than volume. If a straight, or flat roofed transfer is best for peak power, and a angled one increases range, then these bridge ports may help to widen the range of peak power.

 

[old-cat]

Terry that's what I see with the bridge ports too.....more of a change in flow direction than volume. If a straight, or flat roofed transfer is best for peak power, and a angled one increases range, then these bridge ports may help to widen the range of peak power.

I think that's what my little MS260 needs, it loses a lot of rpms when it gets more than a little load on it.

 

[scallywag]

Imagine no compression
It's easy if you try
No saw performance
Without no PSI
Imagine all the people
Freezing all today...

Imagine there's no firewood
It isn't hard to do
Nothing in your pickup
Or in your woodpile, too
Imagine all the people
Paying for LP...

You may say my saw's a screamer
But I'm not the only one
When Randy made my saw
One runnin' son of a gun

Imagine two stroke obsession
I wonder if you can
No more crappy wildthing
Only three saw plan
Imagine all the people
Splitting all that wood...

You may say my saw's a screamer
But I'm not the only one
I hope someday you'll join us
Piss revving so much fun

Did that take long to work up?..........Or did you spontaneously produce it from your exhaust port?

 

[Mastermind]

I pull this stuff straight outta my ass.

Was the ever any doubt about that?

 

[Stihl working hard]

Another very informative thread Randy you are the master

 

[big t double]

.........
Here's another thought. In a two stroke engine, it's all about the time/area of the ports went it comes to performance. You can widen the port to gain T/A, or you can raise it. If the rings travel across the exhaust would it be wiser to get the T/A you want by setting the height, or widening the port?????

was this a rhetorical question? I hope not because id like to take a stab at it...for the sake of discussion. id say it would be wiser to set the height instead of widening. I would think widening the exhaust port would allow more of the ring to drop into the port and beat it up worse and risk it hanging up? but my question is what about the guy that doesn't have the ability to cut a squish band and reset the base...would widening the exhaust port alone net any sort of gains or just be more likely to catch a ring? I know I ask that question without knowing if ive first given a correct answer to your original (possible rhetorical for the more in the know) question....but ive been stewing on this for a couple days now...this is the best I could come up with...flame away!!

 

[Mastermind]

Thank you for adding to the discussion.

First let me say that I do not have all the answers. Sometimes, the more I think I know.......the less I really understand.

Here's my take on it though.

In a work saw that is used to make a family money, or heat their home.........the number one consideration should be reliability. That said, an overly wide exhaust port should be avoided. So getting the height just right seems like the way to go.

Can gains be had from just widening a port? Oh yeah. That was considered a "normal" woods port a few years ago. Just widen the ports, and poke a hole in the muffler somewhere. That was good for a 15 - 20% gain in some cases........but in order to get 35 - 40% gains the builder has to dig deeper than just doing a little Dremel work......

 

[nmurph]

...but in order to get 35 - 40% gains the builder has to dig deeper than just doing a little Dremel and Enco work......

Fixed it for you.

 

[big t double]

Thanks for the response mastermind. Now a question about the intake...I notice that the opening on the bore side gets widened and blended back toward the boot but how does that flow more fuel if the intake boot side stays the same diameter opening...then there's the intake boot itself...it seems to me (a moron by the way) that only so much air/fuel can fit through it...this has always confused me when looking at porting threads. Thanks for taking the time to do threads like this to help idiots like me understand what you guys do a little better.

 

[Mastermind]

It's about how much the port flows when it first opens........that's when velocity is at it's peak. Think about what the port would look like at 20% open.......then notice that the corners really infringe upon open area at that point.

As far as maximum flow........the venturi in the carb is the smallest point in the intake tract.

 

[Chris-PA]

One of the reasons I asked up thread what the manufacturers do is because there is always some trade off. In the case of a flatter lower edge on the intake, I wonder if it creates a stronger, faster rising edge to the pressure pulse that is caused every time the intake port opens or closes. In turn, those pulses may have negative effects on the carb and fuel/air mixture.

 

[Mastermind]

Every move a person makes on an engine is a compromise of some sort.......that is a fact. The flatter intake floor likely hurts fuel economy.

 

[big t double]

It's about how much the port flows when it first opens........that's when velocity is at it's peak. Think about what the port would look like at 20% open.......then notice that the corners really infringe upon open area at that point.

As far as maximum flow........the venturi in the carb is the smallest point in the intake tract.

Ok now it's starting to Makes sense thanks for taking the time. So being wider on the bore side allows it to pull fuel in through the carb and boot at a faster rate due to more time/area. I kinda wanna dremel on a jug hahahahaha