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What is freeport?

Dieselnut77

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Gents, I've been looking everywhere for an answer, but have yet to find one.

I hear a ton of talk about freeport, but no explanation of what it actually is, only that too much can be bad, but none or some can be good, depending on numerous factors.

Would someone be kind enough to enlighten those of us who don't understand it?
 

Dieselnut77

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Thank you for the explanation, Canadian Farm Boy. It's a lot simpler than I'd thought. More for me to chew on....
 

huskihl

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Thank you for the explanation, Canadian Farm Boy. It's a lot simpler than I'd thought. More for me to chew on....
It also applies to the sides of the piston skirt at the exhaust and intake ports. Those are much more of a problem in most cases than what bottom freeport seems to cause
 

Dieselnut77

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It also applies to the sides of the piston skirt at the exhaust and intake ports. Those are much more of a problem in most cases than what bottom freeport seems to cause

Is it because there is such a large area to deal with when both sides of the piston are considered? Also, the area on either side is essentially constant as the poison moves. In contrast the port at the bottom of the skirt is open briefly as the skirt clears the exhaust floor, then closes it on the way back down. Am I close, or barking up the wrong tree? I hope this makes sense.
 

huskihl

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Is it because there is such a large area to deal with when both sides of the piston are considered? Also, the area on either side is essentially constant as the poison moves. In contrast the port at the bottom of the skirt is open briefly as the skirt clears the exhaust floor, then closes it on the way back down. Am I close, or barking up the wrong tree? I hope this makes sense.
We usually try to avoid bottom freeport on the exhaust, but nobody can seem to think of a time when it made the saw run worse. Some say those were their better running ones.

If you freeport on the sides of the piston skirt at the exhaust or intake, it won’t run well at all because you’ll lose all of your primary case compression.
 

Moparmyway

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We usually try to avoid bottom freeport on the exhaust, but nobody can seem to think of a time when it made the saw run worse. Some say those were their better running ones.
I suppose muh Momma nicknamed me Some, but all this time I thought she was sayin "SON" ....... ?????

Count me in the lump of "some" that say "those were their better running ones" !!!!!
 

huskihl

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I suppose muh Momma nicknamed me Some, but all this time I thought she was sayin "SON" ....... ?????

Count me in the lump of "some" that say "those were their better running ones" !!!!!
lol
 

Dieselnut77

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We usually try to avoid bottom freeport on the exhaust, but nobody can seem to think of a time when it made the saw run worse. Some say those were their better running ones.

If you freeport on the sides of the piston skirt at the exhaust or intake, it won’t run well at all because you’ll lose all of your primary case compression.

Makes sense.
 

pbillyi69

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so if you have a saw where there is a small amount of freeport and it runs really good.....does that then mean that a little less case charge is better? i dont know if i asked that right.
 

huskihl

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so if you have a saw where there is a small amount of freeport and it runs really good.....does that then mean that a little less case charge is better? i dont know if i asked that right.
Depends where it’s free porting. If it’s on the sides of the intake or exhaust, you’re losing case vacuum and compression and not pumping as much charge up to the top
 

pbillyi69

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right and does that make them run better? i dont see how it would
 

huskihl

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right and does that make them run better? i dont see how it would
Correct. There’s no way that it runs better if you’re too close to free porting on the sides. Bottom of the exhaust is frowned upon, but doesn’t show poor running characteristics like on the side.
 

pbillyi69

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ok i was making sure there wasnt something i was missing there
 

drf256

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right and does that make them run better? i dont see how it would
The theory for under the skirt freeporting helping is that at the end of exhaust flow there is inertia of exhaust flow and possibly some negative pressure there. The minimal opening may help pull charge into the case.

IMHO, the saws that freeport run better because their geometry is better and the builder has no choice than to drop that jug beyond the piston skirt.
 

pbillyi69

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its too bad that we couldnt see inside a good running engine in super slow motion to see the changes
 

pbillyi69

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i like to free port under my wifes skirt...said in a forest gump voice.... lol
 

Paul Fithian

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I just finished porting a 44.7mm cylinder for an 024 AVS. When viewed from the intake port, a tiny amount of light is visible at the exhaust port when at TDC . Numbers are 96/120/78. I did not notice this before dropping the intake timing to 78.

Saw runs great with good power in the cut.
 
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