just did a compression test on a 350 from a 1991 vette with sportsmanII 72cc heads and I came up with 180psi.
That seems to me like somewhere around 11:1
I thought it was supposed to be around 150psi
with somewhere around 9.*:1
Are my calculations off or does 180psi sound correct for 11:1?

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1990 TA 350 TPI
SPORTSMAN II HEADS
COMP CAMS 224-230@.50
52MM THROTTLE BODY
24LB INJECTORS

 

the psi reading has no or very little relevance to the static compression ratio.

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ICON Motorsports
1st & 3rd
MM Black Diamond 538 F&AM

 

thats good to know. I was expecting lower readings but as long as all of the cylinders were the same I guess its cool.

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1990 TA 350 TPI
SPORTSMAN II HEADS
COMP CAMS 224-230@.50
52MM THROTTLE BODY
24LB INJECTORS

 

The air in the cylinders heats up as a result of being compressed. If you could compress it and then hold it there and wait for it to cool back off to ambient, then the gauge would tell you the static CR. Obviously this is not practical. If the engine is even a little bit warm, the gauge reading can go even higher. An engine with a small cam will give higher readings than an otherwise identical one with a large cam, because the extra duration will bleed off pressure at the beginning of the intake stroke.

All you can do with a compression test os check for consistency. It's highly unlikely that all cylinders would be worn exactly the same amount; so as long as they're all pretty close, odds are the engine is in good shape or at least not grossly defective.

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"So many Mustangs, so little time..."
ICON Motorsports

 

well the consistency was there for sure. THe motor was also warm(have burns to prove it) Didn't even think of the temp raising the compression(there goes Physics class).
my cam and heads were causing me to run rich with the stock chip and my infinite wisdom caused me to drive it like that for a few thousand miles. when i found oil ash on my plugs i thought i washed the rings out of my brand new motor.
all of the cilinders tested within 5psi of each other so I think it is OK.

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1990 TA 350 TPI
SPORTSMAN II HEADS
COMP CAMS 224-230@.50
52MM THROTTLE BODY
24LB INJECTORS