This is probably an Ian question.

With a M21 crank and the big piston making a 720cc engine, what is the compression ratio? I could measure it but am hoping Ian already knows.

I've just returned home from Stafford so haven't had time to look at anything...However, by backworking the calclations the standard 5-1 compression ratio and cylinder capacity of an M21 gives a head volume of 145cc....At 720 cc that figure calculates out at 5.96-1....Ian

email (option): ian@wright52.plus.com