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Compression on smaller saws

Justin Taylor

Justin Taylor

ArboristSite Guru
Joined
Dec 21, 2018
Messages
654
Location
Minnestoa
So i have a poulan wild thing and it ported and everything but it has it feels like to much compression it has around 125 psi without base gasket should i put one back on or not it just seems like it would be holding power back.
 
Ketchup

Ketchup

Professional Stick Picker
Joined
Nov 7, 2017
Messages
563
Age
37
Location
Ward, CO
It seems like either your reading is wrong or your saw is damaged somewhere. Maybe bad rod or case bearings?

125psi stock is common in the clamshells I've messed with. I find the base seal cracks easily on clamshells. I had to re-do the base seal 4 times on a 192t because I increased compression.

125psi shouldn't be hard to pull over. I increased compression in my 201t and couldn't tell a difference pulling it over until the squish band was so tight I was afraid to run it (186psi).
That saw also ran like garbage with so much compression. I backed off on that saw and went back to 155 with a squish of 0.026". It revs higher now, but doesn't give the torque I'm after.

Guys have posted about compression impeding RPM, but mostly in bigger saws. I've seen several ported 346's with compression above 200 that really hold speed in the cut, and people have mentioned smaller saws bearing more compression. Maybe that's related to piston weight?

So I'm confused. My little saws have not responded well to high compression. But I have seen 50cc saws that really do. My own are both above 180 and run great. I suspect I have other issues with my porting and working with stratos, but so far I haven't seen good results from high compression in 35cc and below, especially in clamshells.

I'm going to try more compression with different timing in my top handles, but probably not in a clamshell. Wild Things are totally unknown to me.
 
Huskybill

Huskybill

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May 21, 2018
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I don’t delete base gaskets. I port it. No one is considering that the rod and piston expands as it heats up. Anyway why raise the compression more than it is normally? Move the exhaust port up and arch it, lower the intake port. If you have a piston with a thicker distance to the top ring then assemble it with no ring and mark the piston with a pencil where exhaust port openings are. Remove the piston and chamfer the top of the piston. Advance the timing, mod the muffler.

I took a low compression 325 hp engine and ended up with 299hp at the rear wheels.
Mainly porting and tuning. I used all stock high performance gm 375hp valve train parts. But tuning is the key. I used tuning specs that are unheard of still today. Very few builders know this.
 
trappermike

trappermike

ArboristSite Guru
Joined
Jun 18, 2011
Messages
938
Location
British Columbia,Canada
I've found that in small saws you cannot afford to lose torque or they become absolutely gutless in a cut.Contrary to what I've said about comp. on bigger motors,on little ones I would prefer 150 to 170 psi...if possible,it really increase low and midrange power,do not increase intake duration but widen the port if posible. Ex. duration can be increased 2 to 4 degrees,and widened a little. 2 degrees ignition advance should help too.
 
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