Hey so i have searched around and i found alot of results on what the compression should be and it looks like it should be around 140 for an EVO 9 please correct me if im wrong.

I also heard that cammed cars will show lower compression then a stock car is this true?

i heard that a cammed evo should be around the low 100s

also do the numbers matter that much or is it just to make sure all the cylinders are similar.

Let me know

Thanks

 

any one know?

 

140 sounds about right for Evo 9 due to the MIVEC. Evo 8s have higher compression than Evo 9s do.

I wouldn't be TOO concerned about the reading, but rather the variance between the cylinders (no more than 10-15 variance)

 

How much are you reading currently?

 

just to give you insight i have gsc s1s in my 9 its around 130 with 5psi total variance across the board

My fp4r cammed evo 8 was in the high 130s low 140s after a fresh headgasket ,, those are fairly large cams ..

 

ok so a 9 with upgraded Cams should be still in 130s would it be bad if it was low 100 high 90s?

also does elevation have anything to do with it.

 

My Buschur built 2.0 has a lower compression ratio. Still within variance, but they're all around 110. For what it's worth.

 

is 110 bad? or is that normal for a cammed EVO?

Also i was thinking higher elevation = thinner air

does that mean at high elevation you can run more boost then you could at sea level because the air is less dense?

 

This may be an uninformed question, but why would a cam affect compression. Aren't the valves closed during compression? Don't cams only affect the degree of which a valve would open? I know in rotors with a very aggresive port sometimes the exhaust port would remain open almost always but I did not think this was the case with piston motors.

 

damn that is some low #s. did a comp. check on my 8 w/ hks 272's when I found my bad cyl. I was at 150 across except in the bad one which was 120.

 

wow... that 120 cylinder i gona kill your performance....

 

That is one way of putting it hahah...engine has since been rebuilt almost done with break in. did a test after first oil change and it was 160, 145, 155, 160. that was only after 250 miles, so not bad for an engine that has not been seated yet.

 

1) Should be around 140

2) Cams should not change compression because the valves are closed when doing a compression check

3) They should all be relatively the same. They should all be around 140. If one is lower than it shows premature wear in that cylinder. If it is lower in all the cylinders than it shows wear in all cylinders. They should all be 140.

4) If you have a lower compression do a wet compression check. This is squirting some oil in the cylinder. If the compression increases then drops after a while you have a worn piston rings. The oil will sit inbetween the cylinder wall and the piston wall and when the oil gets past the compression will then lower again.

Good luck. Hope this helps.

 

well excluding ur one bad cylender mine reads 150 psi all cylenders too with hks 272's

 

so it seems like cams shouldnt affect compression at all.

Thanks for the help guys