Heart head compression question-gear head math

nkaminar said:
Gene, The displacement of each cylinder is 201/4 or 50.25 cubic inches. It will be a little more if the engine has been bored, but not much and not enough to worry about. Lets say you measure the oil to fill the combustion chamber to be 7.7 cubic inches. Then the compression ratio would be 50.25/7.7 or 6.5 to 1. If you measured 12 cubic inches to fill, then the compression ratio would be 50.25/12 or 4.2 to 1. There are lots of errors that can creep in so one decimal place in the compression ratio is all that can be expected.

Make sure the piston is at the top and both valve are closed. That would be cylinder 1 with the pin in the detent in the cam gear. Also, fill the oil to the bottom of the spark plug hole, not the top.

It would be best to suck the oil out rather than let it escape out the exhaust manifold. Some will escape anyway and will create a lot of smoke when it starts to burn off.
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Stay tuned readers, I'll fill number one cylinder up this next week with some Marvel MO or 30 weight engine oil using a syringe to measure with and report back on this thread.
 
cars2cool said:
Stay tuned readers, I'll fill number one cylinder up this next week with some Marvel MO or 30 weight engine oil using a syringe to measure with and report back on this thread.
Click to expand...

okay I just got done doing my measurement of the #1 cylinder with a syringe given to me by my pharmacist friend. The measurement is in cc's. I came out with 165cc's. Both the head and the block surfaces have been milled or planed for flatness and the block was bored .060 oversize. Okay now what does this calculate for an estimated compression ratio of my cylinder head?
 
That would be about 5:1 give or take



50.165 ci cylinder with .060 over and 10.065 ci combustion chamber
 
Actually, there is conflicting information out there as to the exact stroke of the engine. Some say 4.125 and others say 4.25. I believe the latter is correct. That would make the cylinder volume 51.685 CI giving an actual compression ratio of 5.135:1. That’s close enough to the police head’s advertised 5.22:1 for me.
 
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