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1st, I know that the devil is in the details.... Cam plays a part. Use plays a role. etc. I am looking at head gaskets for a 547... 4.5 bore/4.3 stroke A-headed engine. Flat top pistons and 79cc chambers. I have some SCE copper gaskets on it (.072), but that is about 12-1. Cometic has some thicker gaskets, but I don't want to go any thicker than I have to. Use will be street/strip. Mechanical roller, carbureted, naturally asperated. What is the maximum C/R I might get away with pump gas (93)? How much overlap is required to keep 12-1?
 

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12 to 1 on pump gas with a .070+ squish even with a 260++ intake lobe is going to be tough.

We've run 11.7 to 1 on pump gas with tight quench and those duration numbers and higher but the tuning window is really narrow.







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+1. Large quench lowers compression but tends to increase detonation. Build it with good factors and practices for the chosen fuel, or feed it with good octane to suit the build.
✅ Pick one.
 

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Keep in mind also that on line calculators never factor in the ring land volume which with a motor of your bore size I bet will add another 2 CCs to your overall volume above the piston.

With your CID motor every 4 CCs up or down is darn close to a 1/4 of a point change in compression.
 
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