Chainsaw Porting Theory

[jmssaws]

And an 026 is nothing to be ashamed of ,its not the size of your saw ,but how you use it to get the job done .

Thanks man.

 

[drf256]

Thanks man.

Brett probably meant the exhaust port J.

 

[merc_man]

If the intake already has a nice size and shape, remember, you can add intake duration by trimming the piston skirt.

What exactly is intake duration? The amount of time its open or closes?

 

[drf256]

What exactly is intake duration? The amount of time its open or closes?

open

 

[GoBigBlue1984]

Open, I'm sure others can go into greater detail but I've always looked at it like this, more duration/more it can breathe.......to a degree that is. Too much is counter productive. Poor throttle response from my experience.

 

[merc_man]

Open, I'm sure others can go into greater detail but I've always looked at it like this, more duration/more it can breathe.......to a degree that is. Too much is counter productive. Poor throttle response from my experience.

How do tou determine the max duration to aim for.

 

[merc_man]

Good to see this thred active again[emoji6]

 

[jmssaws]

You want your intake and exhaust as close to square or square.

Meaning if you have 160 exhaust duration or 100 degrees you want 160 intake duration or 80 degrees.

 

[idiotwithasaw]

If the intake already has a nice size and shape, remember, you can add intake duration by trimming the piston skirt.

IF the jug has already been lowered .030 or more. What would I gain by adding more?

 

[idiotwithasaw]

You want your intake and exhaust as close to square or square.

Meaning if you have 160 exhaust duration or 100 degrees you want 160 intake duration or 80 degrees.

Took me a minute, but I think I understand.

 

[jmssaws]

Took me a minute, but I think I understand.

It's not a must but the closer you are to square the better.

 

[smokey7]

Good laughs guys I enjoyed the jokes thanks. I'll think about beveling and port shapes when in bed later tonight .

 

[SawTroll]

Regardless of exact "porting numbers", there has to be a balance between the carb, intake, transfer capacity and muffler - but there is more to it as well. What many "saw builders" miss (and is in denial about) is the carb part, as it makes the mods more expensive and complicated.

 

[paragonbuilder]

Regardless of exact "porting numbers", there has to be a balance between the carb, intake, transfer capacity and muffler - but there is more to it as well. What many "saw builders" miss (and is in denial about) is the carb part, as it makes the mods more expensive and complicated.

Can you elaborate?


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[jmssaws]

Numbers are exactly what they are, just numbers.
10 builders can build the same saw with the same numbers and all 10 will run different.

As far as carb mods go,the stihls and big huskys I do haven't needed a carb upgrade. Most ported saws tune almost the same as a stock one so I fail to see why the carb needs modded. If I was 2 turns out or something then maybe.
For a strong work saw its completely unnecessary on most saws.

 

[Chainsaw Jim]

Can you elaborate?


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.........lol

 

[GoBigBlue1984]

Regardless of exact "porting numbers", there has to be a balance between the carb, intake, transfer capacity and muffler - but there is more to it as well. What many "saw builders" miss (and is in denial about) is the carb part, as it makes the mods more expensive and complicated.

What he's saying I understand but I don't. I've had "saw builders" tell me the same thing. It all goes back to what Jerry branch always preached. It's not about what you take out of the cylinder or do to it. It's more about what you pump into it. I know, I know some of you will say that we're talking two different animals here, but it's all relative in principle. There's much I don't know and understand but that's why I'll work my ass off to try to crack this riddle. There's always more to be had. But yes, please elaborate Saw Troll. I'm interested to hear your take on this. I'd love for @Terry Syd or @Poleman to contribute to this carb discussion as well.

 

[mdavlee]

Intake tract on a 65cc husky is bigger than a 92cc stihl. You can gain with carbs but it's such a pain to swap on some saws that it's not worth the hassle.

 

[Chainsaw Jim]

I've seen a hda carb meant for a 56cc saw run a 72cc top end about as hard as one can be ran without a tuned pipe. The metering seat and main nozzle were drilled out a little bit.
A larger venturi isn't always the ticket.
What saw troll is likely trying to say is the velocity running through the carb pulls the fuel so you better have enough pull for a larger venturi to function at its potential. That's why carb matching can be costly if you don't have a pile of them to work with.

 

[CR888]

Many think 'my saw four strokes at xxxxRPM' so it can't be improved, its delivering enough/more fuel than my saw can combust properly so its as good as it gets. WRONG. Certain changes can greatly improve a saws torque right through the rpm range. I especially notice the torque down low and light switch throttle response. I agree not enough thought/modification is considered toward carburation when builders port saws. Very decent gains can be had from improved carburation alone.