Chainsaw Porting Theory

[sawmikaze]

A 660 can't work well with a popup but I'm sure some saws can were the exhaust don't need lowerd.

I had a 461 dan henry ported that had a pop-up..i called that saw the eliminator..it embarassed a few saws in its class with other porting configurations...i dont wanna see anyone argue over this..i really wanna know the answer.

 

[jmssaws]

Ya ive been told that many times..

Im still curious why on other models.

If you don't have to lower the exhaust a popup works just the same as cutting the chamber only you have to machine a new piston to replace it. There is no difference other than that.

 

[sawmikaze]

If you don't have to lower the exhaust a popup works just the same as cutting the chamber only you have to machine a new piston to replace it. There is no difference other than that.

I see...this is something thats made me wonder over the last few years and totally contradicted itself for me many times over , ive asked many guys and never got an answer...im seriously interested in why people say it doesnt work.

 

[jmssaws]

I see...this is something thats made me wonder over the last few years and totally contradicted itself for me many times over , ive asked many guys and never got an answer...im seriously interested in why people say it doesnt work.

All it does is raise compression just the same as cutting the chamber, the only saw it won't work on is one that needs the exhaust lowered. I can't make enough compression with one for the way I port.

 

[jacob j.]

The argument against pop-ups is that the pop-up interferes with the flame front, and that may be true to some extent but I doubt it's enough to really affect scavenging to the level some people say it does. Several saws came from the factory with pop-ups which doesn't mean it's the best practice but it was a widely accepted design feature for many years in the industry.

One of the basic ideas about domed pistons is to increase the surface area of the crown for the charge to push down on- you'll see this a lot in engines designed to make their power at a lower RPM range and typically they have low, flat, wide port timing and shapes.

 

[sawmikaze]

The argument against pop-ups is that the pop-up interferes with the flame front, and that may be true to some extent but I doubt it's enough to really affect scavenging to the level some people say it does. Several saws came from the factory with pop-ups which doesn't mean it's the best practice but it was a widely accepted design feature for many years in the industry.

One of the basic ideas about domed pistons is to increase the surface area of the crown for the charge to push down on- you'll see this a lot in engines designed to make their power at a lower RPM range and typically they have low, flat, wide port timing and shapes.

Thanks for makin me feel even dumber.

 

[Moparmyway]

One of the things that a pop-up does is alter the transferr flow ..... instead of washing across the entire crown, it is directed off the surface of the piston and into the chamber untill the piston moves down in the bore enough to clear the pop-up away from the transferr port

My pearls of wisdom are now shot for the rest of the week ................. thats all I got

 

[jmssaws]

The only reason I cut chambers is if the guy I ported the saw for in Oregon needs to replace the piston he can use a stock oem piston,it makes way more sense for a porter to cut the chamber because of that no matter If one is better or not.

 

[sawmikaze]

The only reason I cut chambers is if the guy I ported the saw for in Oregon needs to replace the piston he can use a stock oem piston,it makes way more sense for a porter to cut the chamber because of that no matter If one is better or not.

Cant argue the ease of just swappin pistons.

I just laugh when guys that use their saws for a cord of wood on the weekend are concerned with the ease of swappin pistons..they couldnt wear out a 170 in 25 years.

Its not much of an issue for me , i have to order a piston anyway since my dealer doesnt stock them and then i can have one of our fine members cut me one or go to the machine shop 2 miles from my front door.

 

[quietfly]

What i would like to know is what is different when porting for something like a milling saw vs something like a racing saw or even an every day limbing/cording saw.

 

[shorthunter]

If you don't have to lower the exhaust a popup works just the same as cutting the chamber only you have to machine a new piston to replace it. There is no difference other than that.

Squish velocity ???

 

[Moparmyway]

Its not much of an issue for me , i have to order a piston anyway since my dealer doesnt stock them and then i can have one of our fine members cut me one or go to the machine shop 2 miles from my front door.

The only issue I see in this line of reasoning is that one would need to know a bit of information about their pop-up

How deep to cut the piston
How wide to keep the pop-up
What angle is the cut section (if any)
What is the radius angle of where the cut section meets the pop-up

 

[rocketnorton]

subbed

+1

 

[leadfarmer]

I think I just got a pop up [emoji38] [emoji38] [emoji38]

 

[Four Paws]

Here is where the rubber meets the road

@David Young

 

[jmssaws]

Squish velocity ???

Beats me

 

[jacob j.]

Thanks for makin me feel even dumber.

I feel that way when I see Randy, Jason, Scott, Shaun, Carl, Al, and our other talented builders discuss theories. Hey guys! wait up!

 

[sawmikaze]

The only issue I see in this line of reasoning is that one would need to know a bit of information about their pop-up

How deep to cut the piston
How wide to keep the pop-up
What angle is the cut section (if any)
What is the radius angle of where the cut section meets the pop-up

Wouldnt they just measure my old piston ?

 

[jmssaws]

I don't see the point of adding cost to the new piston plus the time of getting it done. It's no problem for me but for lots of people it would be.

I'm not against a popup i just don't see the point in it.

 

[Tor R]

I am probleby one who would set porting away to one porter, and I would prefer porting without pop up.
The way I see it, jug last longer then piston.