compared some compresion

[Yotaismygame]

I have a thread on the other site about this exact issue with testers. I have two testers, one with a long hose and one short hose specifically for small engines and they read within 5psi of each other. I ported a 550xp and the before and after compression readings were the exact same at 135, makes no sense. A makita I just finished read 155psi but its pretty damn hard to pull over. My initial guess was about 180-190. On this other thread some guys mentioned how the starter recoil is setup, and then again of course piston size makes a difference. I'd prefer to never test compression again but people like to see those numbers when buying a ported saw. It's hard to say well the gauge says 155 but it sure feels like 180....

Nobody seems to really know the answer to this issue.

 

[old guy]

I have a thread on the other site about this exact issue with testers. I have two testers, one with a long hose and one short hose specifically for small engines and they read within 5psi of each other. I ported a 550xp and the before and after compression readings were the exact same at 135, makes no sense. A makita I just finished read 155psi but its pretty damn hard to pull over. My initial guess was about 180-190. On this other thread some guys mentioned how to starter recoil is setup, and then again of course piston size makes a difference. I'd prefer to never test compression again but people like to see those numbers when buying a ported saw. It's hard to say well the gauge says 155 but it sure feels like 180....

Nobody seems to really know the answer to this issue.

I hear ya, my new gauge brought that 372 up quite a way.

 

[Lightning Performance]

I have a thread on the other site about this exact issue with testers. I have two testers, one with a long hose and one short hose specifically for small engines and they read within 5psi of each other. I ported a 550xp and the before and after compression readings were the exact same at 135, makes no sense. A makita I just finished read 155psi but its pretty damn hard to pull over. My initial guess was about 180-190. On this other thread some guys mentioned how the starter recoil is setup, and then again of course piston size makes a difference. I'd prefer to never test compression again but people like to see those numbers when buying a ported saw. It's hard to say well the gauge says 155 but it sure feels like 180....

Nobody seems to really know the answer to this issue.

The answer is knowing the complete combustion chamber volume, including the piston top if popped or dropped, the quench volume and the swept volume of the piston from the top of the exhaust port, not the stroke. Then you can figure out the static compression ratio. Four cycle engines will not be the same. After you figure all that toss your numbers in a trash bin. Engines run on dynamic compression not static ratios. They are different. Nuff said?

Edited