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compression ration vs psi

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Old August 15th, 2015, 07:59 PM
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compression ration vs psi

Question for you physics majors. I recently checked the compression on the 68 455 engine I am installing. The readings for a cold block with all plugs removed and no carb on the intake were between 190 and 200 psi for each cylinder. How does PSI relate to CR? The engine has C heads with new valves and was bored .030, previous owner was not sure what pistons or head gaskets were used. Thanks to all
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Old August 15th, 2015, 08:35 PM
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Originally Posted by 67Rocket
How does PSI relate to CR?
It doesn't.

It relates to CR and cam profile and timing.

Without knowing the details of the cam, it is impossible to suggest an exact cranking compression number.

That being said, your numbers are normal for a '68 engine, and probably represent a high compression engine.

- Eric
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