The MGA With An Attitude

For measuring compression ratio, the best method is to have a piston at TDC on the compression stroke and quickly add oil through the spark plug hole. This measured combustion volume is added to the swept volume (area of bore X stroke), and divide the measured combustion volume into the volume of the total previously calculated. Remove oil by siphoning and turning the engine over many times with the spark plug still out to avoid damge due to hydraulic lock.

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