Compression, PSI to Ratio conversion?

Hey guys,

I have an X1 with the 43cc engine. Does anyone know what the convesion from psi to compression ratio is. I am showing 138psi on my gauge. What does that convert to.

I am looking to get 13:1. Does anyone know how many psi that would be?

sorry but that is not how it works at all. 13:1 is impossible on a 2 stroke unless you are measuring static compression but the accurate way to measure the 2 strokes compression ratio is from the time that the piston passes the exhaust port. That is the way most manufacturers measure it which is why most literature on 2 stroke bikes will specify a compression ratio of 6.5-1 up to 8-1. 138psi is pretty high if your motor is stock and your gauge is accurate, try someone else's compression tester to see if you get the same high result.

Hey Bart,


I tried another tester and I got 90psi, but was having trouble getting a good seal because it was longer than the other one and was hard to get in there. I was showing 119psi befor I took the engine apart. When I put it together I did not use a gasket so the comp should have raised a little.

Also this site sells a 13:1 that runs on 93 octane. http://www.pocketbike-warehouse.com/...tml&lang=en-us I wanted to try to run the same comp on my stock little motor.

What I am trying to do is run the most compression possible with 93 octane. That is my goal. I am using 87 octane right now, and am worried that it is too low for the comp I have.

Compression testers are only good for a ballpark figure or to compare multi cylinder engines to see if they are even across the board. I have never had 2 testers read the same thing but I never had a very expensive one either, I typically get readings of 90-100 on stock motors with my tester. The 13:1 ratio is not very accurate but will certainly be higher than stock, you want to find a dome with a wide squish band and a central spark plug to be able to run lower octane with high compression. The spark plug location stock will certainly detonate with low octane but a centrally located spark plug with a wide squish band dome will tolerate less octane with higher compression, you may be able to go even higher compression on 93 octane if you set it up right.

I didnt think the tester would give an accurate reading, though I can see how the compression changes. That way I can see the difference. By the way. I noticed absolutely no difference in speed from the 120 psi to the 140psi. I will let you know if changing my fuel will help.