Can I figure out what the compression ratio of a 400 cid motor is using a compression gauge? Is there a direct relationship between PSI and CR?

Thanks,
Steve

 

I'm not sure I get what you're saying...

Are you saying that due to pressure loss around piston rings, the gauge might be inaccurate?

 

I figured that the PSI reading wouldn't account for pressure lost due to cam duration...

Basically, I've come into posession of a 67 Camaro with a 400 cid motor that was clearly built to be a 1/4 mile car... (Roll bar, fuel cell, stripped bare for weight reduction, M/T drag slicks) but I don't have any specs on the engine internals... I have started it up and it will idle (VERY CHOPPY) on 93 octane, but I don't know if the motor was built for race gas only... This thing is in no way street legal....

Short of driving it hard and listening for knock... How can I figure out what fuel I should be running?

 

the only way to know for sure is by removing the cyl. head and mesuring the cc's of the combustion chamber and piston area at tdc. - of if you know the part # of the piston.
best bet run 50/50 racing fuel and prem.
good luck