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New guy hoping for good advice. I was finally ordering a rotating assembly when the salesman said I could only have either 9.3 or 10.8 compression ratio. Stopped me cold. Reading these forums has convinced me that 10:8 is too much. It will be a premium pump gas street car, GM performance aluminum oval port heads, 496, FORGED pistons. He checked JE, SRP, WISECO, and maybe another brand of pistons. I think the CRs above were SRP's. Milling domes or heads would be my last choice. Any other brands of (off the shelf) pistons that might have a small dome ? Would thick gaskets lower it enough to justify the "quench" problem? 4.25x4.310, 6.385 rod. Thanks.
 

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floppers forever
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ARW said:
New guy hoping for good advice. I was finally ordering a rotating assembly when the salesman said I could only have either 9.3 or 10.8 compression ratio. Stopped me cold. Reading these forums has convinced me that 10:8 is too much. It will be a premium pump gas street car, GM performance aluminum oval port heads, 496, FORGED pistons.
10:8-1 is fine if you have aluminum heads.
 

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ASE Certified Master Machinist
1967 Chevrolet Biscayne 10-71 blown 433 Big Block Chevy, T400 & 12 bolt 3.73 rearend
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Nitro is correct. With aluminum heads, you can run a full point higher compression than you could with cast iron heads. A 10.8 compression ratio will work fine.
Make sure to keep the quench at .040-.045. Proper quench matters more to detonation resistance than a slightly lower compression ratio.
An 11-1 compression ratio with proper quench will be more detonation resistant than a 10-1 compression ratio with insufficient quench.
 

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Hammer and a torch
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What the guy was meaning (selling the rotating assy.) was if you have open chamber heads then the compression ratio will be 9.3 to 1 and if you have closed chamber heads then its the 10.8 to 1 so what you should have is the 9.3 to 1 since most all GM performance BBC heads are open chamber... Closed chamber went out back around 1968-69 and since then open chamber was used mainly because of the better combustion and emissions... But...! There were some semi-closed chamber heads that were cast that are some rare sought after items... If you use a small dome piston you get a very nice even flow and flame travel... Like using a flat top piston in a SBC... :thumbup:
 
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