Chainsaw Porting Theory

[drf256]

I'm still amazed how they run with the exhaust that low and the huge intake duration.

If it has a relatively large case volume, a lower exhaust is creating a larger saw.

 

[drf256]

The 240 saw has 030 off the key and the other is 020.
I don't think detonation is very feasible in a saw, to a point the more compression and ignition advance you can run will yield the most power, depending on the saw of course.

I wonder if advancing the lower comp saw more would add rpm and power.

 

[jmssaws]

If it has a relatively large case volume, a lower exhaust is creating a larger saw.

I'm not going to tell his numbers but the intake duration is bigger than any running saw I've heard of. And it's hands down the most powerful small saw I've ran,faster than a much larger saw.

 

[jmssaws]

I wonder if advancing the lower comp saw more would add rpm and power.

Seems on a 660 more ignition slows it down.

 

[awol]

My bet is very little blowdown.

AWOL, what's the answer?

VERY little blowdown, around 8 degrees on my latest 562. This is only possible because of the extremely high case pressure in these saws, and a very wide, square exhaust port. I think that's one reason why we see so many blown case gaskets, blown seals, blown base gaskets, and leaking trans covers.

 

[drf256]

I'm not going to tell his numbers but the intake duration is bigger than any running saw I've heard of. And it's hands down the most powerful small saw I've ran,faster than a much larger saw.

I would never expect you to divulge another builders numbers.

 

[drf256]

VERY little blowdown, around 8 degrees on my latest 562. This is only possible because of the extremely high case pressure in these saws, and a very wide, square exhaust port. I think that's one reason why we see so many blown case gaskets, blown seals, blown base gaskets, and leaking trans covers.

Ahhhh....

I see (said the blind man)

 

[jmssaws]

Ahhhh....

I see (said the blind man)

One of my dad's many sayings.
My favorite one is "slick as a minnows dick"

 

[Moparmyway]

Ahhhh....

I see (said the blind man)

I see that there is no way to put a rule on this exhaust thing ................ each saw makes its own rules

 

[awol]

No secrets here. I kinda doubt that I've done two 562s that have exactly identical numbers, I haven't even had a wheel on my last 5 saws! I would say though, the numbers are near:

Ex 110
In 83
Trans 101

 

[jmssaws]

I thought the intake was in the 90's? My bad

 

[Mastermind]

Alan......I'm sure glad we have you to add your knowledge to these conversations. Thanks for hanging out with us.

 

[drf256]

The mutual respect we have for each other here is what's fueled this sites growth IMHO.

It just wasn't there on the AS.

 

[jmssaws]

Alan......I'm sure glad we have you to add your knowledge to these conversations. Thanks for hanging out with us.

I completely agree randy,I spent most of a day with Alan and he is a fascinating individual.

 

[jmssaws]

The mutual respect we have for each other here is what's fueled this sites growth IMHO.

It just wasn't there on the AS.

Whats as?

 

[awol]

I thought the intake was in the 90's? My bad

The 90s saw is my 3 cube racer; with 185 degrees of intake, the throttle response and low end torque is still amazing!

The 562s, (or any strato for that matter) dont need a lot of intake duration, because they have ports that equal up to 125% of bore width. Thats a lot of area increase over a conventional single intake port. I just leave the floor where it falls after dropping the jug.

 

[drf256]

No secrets here. I kinda doubt that I've done two 562s that have exactly identical numbers, I haven't even had a wheel on my last 5 saws! I would say though, the numbers are near:

Ex 110
In 83
Trans 101

Great numbers.

So you lowered case pressure.

Raised the uppers to compensate for the lowering of case pressure and the larger volume you needed to fill the larger cylinder of volume you created with the lower exhaust.

THIS STUFF fascinates me. The WHY of it and not just the HOW.

 

[drf256]

Now I need a strato saw. Damn CAD.

 

[awol]

Great numbers.

So you lowered case pressure.

Raised the uppers to compensate for the lowering of case pressure and the larger volume you needed to fill the larger cylinder of volume you created with the lower exhaust.

THIS STUFF fascinates me. The WHY of it and not just the HOW.

Yup, and by doing it this way, effectively increase the available power stroke by a substantial margin.

 

[Mastermind]

A few years ago all the pundits were saying raise the exhaust........always raise it.

My how things change.