Is freeporting good or bad?

[Chainsaw Jim]

I've read a lot about freeporting being a bad thing. I've also heard old school saw builders mention it like it's a big secret for hopping up saws.

 

[drf255]

I think that when it's a byproduct of other machining to make more power it appears to enhance performance, when in fact, it's the other changes.

Most of the pros here have said that a little won't do anything bad. I dont think intentionally causing freeporting will do anything for performance gains, in and of itself.

Most of the Stihl's I've played with are limited to grinding because of it.

I feel Husky jugs are WAY better designed to allow performance enhancements, period. I find their build quality subpar to Stihl's though.

 

[drf255]

Would be an easy experiment to take some metal off of the exhaust side skirt of a piston and see what it does. Back to back with a stock one. No other changes to the saw.

 

[Chainsaw Jim]

I'm wondering if the freeport can act as a vent to allow more mix into the case after modifications have been made.

 

[SawTroll]

I have never heard or read anything positive about free porting, from anyone that is supposed to know what he is talking about - only negative.

 

[jmssaws]

I have a stihl 66 cylinder that Freeports a bunch and runs strong, it probably doesn't help but it's not detrimental either.

A big husky has lots of piston and a stihl doesn't but both can be equally strong.

 

[KG441c]

I'm wondering if the freeport can act as a vent to allow more mix into the case after modifications have been made.

I agree with that in that it would also reduce some spitback too. Probably on a smaller capacity crankcase such as a 440/460 hybrid it may help alil

 

[jmssaws]

Freeport to a point don't hurt anything, I won't say it helps but I sure don't hurt.

 

[Chainsaw Jim]

I'll have to measure again to be sure, but my 372xpw was mistakenly freeported by about 1/8th inch. I thought I ruined it but I bolted it down anyways and it ended up running and cutting very well.
I was hoping someone would know the science behind what actually happens when freeporting occurs.

 

[KG441c]

I'll have to measure again to be sure, but my 372xpw was mistakenly freeported by about 1/8th inch. I thought I ruined it but I bolted it down anyways and it ended up running and cutting very well.
I was hoping someone would know the science behind what actually happens when freeporting occurs.

Seems if u have a small crankcase capacity and alota intake duration that would cause some spitback, alil freeporting may help vent off the unneeded supply?

 

[KG441c]

Seems it would in my mind maybe increase rpm but take alil torque away?

 

[Duane(Pa)]

Cool thread! Can you tell if a saw is freeporting by exhaust sound. I have a saw that sounds like the gurgling growl of a Detroit Diesel every once in a while.

 

[KG441c]

Just take the muffler off and rotate piston to TDC and look for any clearance between piston skirt and bottom of exhaust port

 

[Deets066]

Atomized fuel spitting out the muffler instead of being burnt in the combustion chamber doesn't sound like a performance mod to me

 

[KG441c]

Atomized fuel spitting out the muffler instead of being burnt in the combustion chamber doesn't sound like a performance mod to me

Probably not but I wonder if its any worse than it being spit back out into the air filter and housing? If needed and u have excessive spitback means extra fuel in the space that u have to cram it into? Alil bit of vent on the other end of the system instead of back through the carb may let the crankcase fill to its max potential per cycle? Just thoughts in my head and throwing ideas around only

 

[Deets066]

Probably not but I wonder if its any worse than it being spit back out into the air filter and housing? If needed and u have excessive spitback means extra fuel in the space that u have to cram it into? Alil bit of vent on the other end of the system instead of back through the carb may let the crankcase fill to its max potential per cycle? Just thoughts in my head and throwing ideas around only

Possible

But how I see it spit back occurs when your still dumping fuel into a full crankcase. Now you have a full crankcase you need to transfer all of the fuel into the combustion chamber. This cannot happen if some is goin out the exhaust.

Just my theory though

 

[KG441c]

Possible

But how I see it spit back occurs when your still dumping fuel into a full crankcase. Now you have a full crankcase you need to transfer all of the fuel into the combustion chamber. This cannot happen if some is goin out the exhaust.

Just my theory though

Thats my point. If its full it will push backwards but if the system had alil vent on the other end of the spectrum would it allow it to fill completely during the transferring also?

 

[Deets066]

Thats my point. If its full it will pish backwards but if the system had alil vent on the other end of the spectrum would it allow it to fill completely during the transferring also?

I smell what your steppin in now. Yeah that could be, but you still have to be able to burn all of it for it to do any good

 

[KG441c]

I smell what your steppin in now. Yeah that could be, but you still have to be able to burn all of it for it to do any good

Dont know for sure just thinkin but I know I built a saw that has .010 freeport and its a runnin son of a gun!!

 

[mdavlee]

.005" is about 10° at TDC probably. It won't have time to let much out.