Take a 1956 354 Hemi block and crank. Bore to 392 bore, add 9.25:1 392 pistons. Cap it off with 1954 331 Hemi heads (unknown part number on the heads) . What would you guess the approximate compression ratio to be?
Thanks, Anthony. I did see that. I believe that the info in that thread you pointed out is based upon the use of 354 heads. I'm using 1954 331 heads. I'm not sure the chambers are the same size. I recall reading that the use of 392 pistons in a 354 will result in a lowered compression ratio due to the shorter stroke. However I don't know what the use of 331 heads, which I have read have smaller chambers than 392 or 354 heads, will do to restore some of that compression back to the mix. There's too many moving parts to the formula and conflicting info found in my search for my relatively inexperienced head to solve the riddle. Hopefully an experienced early Hemi guy can chime in with some factual info on my setup to be.
There’s compression calculators on line you can put your numbers in and get an idea of what you will have. I have a set of 1556157 331 heads that I CCd at 100 cc. The factory steel head gasket is .022. You no the bore and stroke you just need to figure out the plus or minus cc of the pistons you plan on using.
•The 331 head should have 100-105 cc. •The 392 piston has a smaller dome than the 354 in order to compensate for the larger swept volume (with similar final c/r). Also, the 392 head has a chamber volume of 110-112cc. This accounts for a nominal 9.25c/r In years past I had such a project and measured the 1" down fill volume and calculated c/r but cannot find that build sheet. IIRC, the new assembly came in at 9:1 with '58 pistons (10:1) but cannot guarantee such.
Hmm, if I understand correctly, assuming your memory is correct, you believe you got 9:1 using 10:1 392 pistons. The pistons I'm thinking of using came out of a 9.25:1 392 engine, so I assume they have a smaller dome? If that's correct, then the compression ratio on my engine would be even lower than 9:1. Does that sound correct?
That would be good logic. Obviously, you cannot get real numbers without actually completing at least one cylinder to check volumes. I'll dig a little deeper for my old build sheet. I'll let you know if I find it.
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