Compression ratios

[basement]

Is there an accurate method for finding out what the compression ratio is in my 360 while the motor is still in the car?

[zerfetzen]

Is it inaccurate to use a compression tester?  If not, you can pick one up for $20, I'm sure.  Let's see what the pros say...

[MEK-Dangerfield]

You can get a compression gauge cheap to test the compression of each cylinder, but I don't know how you would figure out the ratio. 

  Mike

[Chryco Psycho]

a compression guage only measures trapped air at low rpm / cranking speed , , in theory a 10:1 compression engine should read 14.7 atmospheric pressure X10 or about 147 Lbs but at low cranking speeds & especially with long duration cams a lot of the air can escape without being compressed , at higher rpm a good cam can actually overfill the cylinders & mildly supercharge the engine
 the real answer si no you need to disassemble & measure to be sure

[Oldschool]

    Also--altitude will also vary your compression gauge reading.  14.7 is at sea level. Pull it apart and measure, then you're not guessing.      ........Oldschool