Quote:
Originally Posted by Tom Foster
Compression (PSI) / 14.7 = compression ratio. Good for rough estimate, no lab glassware needed.
Fearless
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That would be a very rough estimate! Nowhere near accurate! Compression pressure is dependent on several variables such as when intake valve closes, cranking speed, engine temperature, and rate of leakdown.
Compression ratio, on the other hand, is based on two simple measurements: the volume of the combustion space with the piston at BDC, and then the combustion volume with the piston at TDC. Then simple division gives you the correct ratio.