[MJN]

Perry

Perry I calculate you would have approx 10.95:1 compression ratio just by changing the heads assuming every thing else remained the same. Sounds like it could be a good swap to me depending on the cam duration you are running. You would definitely need to run premium gas.

The detailed formulas can be found by searching on line but basically compression ratio is the total cylinder volume at bottom dead center divided by the total cylinder volume at top dead center. Once you have figured out the relative volumes you can just subtract 26cc (the difference in the chamber volumes) from the volume at top dead center and back calculate the new compression ratio.

The single cylinder swept volume on a 460 (7538cc) is 942cc
so to get an 8.8:1 compression ratio

volume at bottom dead center / volume at top dead center = 8.8

volume at BDC = swept volume plus "chamber volume" / "Chamber volume" (Where the chamber volume is the volume at TDC.)

The chamber volume is the cylinder head chamber volume plus the other volumes above the piston such as valve reliefs, head gasket etc.

So to get an 8.8:1 CR your TDC volume must be 120.75cc

(942+120.75)/120.75 = 8.8

Now to calculate your CR with the new heads just subtract 26 cc from the 120.75 number and re calculate

(942+120.75-26) / (120.75-26) = 10.95