yet another race gas vs. compression question

[rwhitlock]

Hello all...

Looking for some help and opinions on this one. My '97 CR 500 has a compression reading of 150psi. The engine was cold when taken, and the tester was the kind where you cram the rubber cone into the spark plug hole, not the screw in kind. Sorry, but that is the best equipment I could come up with at the time. So I think the warm reading with a better tester would be closer to 180 ?

Anyway, I am looking at running 100 octane race gas. Just wondering if this compression reading is ok for that or if I need to run lower octane.

Thanks,

Rod

 

[Faded]

No 'need' to run lower (or higher) octane gas, pump gas would be sufficient. With the right jetting race gas will get you better throttle response, more consistent results (because the gas itself is more consistent) and ultimately more power. Simply dumping it in the tank won't help. Compression should be tested on a cold motor with the throttle open.

 

[bclapham]

yep, just run the best gas you have. i run race gas and was obsessed with rasing the comp. via head mods, but after i had the head turned down, it didnt want to rev out as much.

one little note, dont rely on a comp reading for piston life, you can still have good comp on a piston that is ready to go bye bye!

 

[Faded]

Yo B,

No doubt on the good compression/bad piston senario. Removed a stock piston from a '98 CR250 (4yrs!) that was still making around 170psi of compression. The skirts had visible cracks in them and you could tell it was about to really start coming apart. :scream: