Thread: unsure of head choice

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O.K., I'll step up and take a shot.....
If we assume a 0.030" overbore, then the cylinder is 727 cc's. Assuming a 0.040" gasket, the volume there is 8 cc's. Assuming the piston is down in the bore by 0.040" at TDC, that's also 8 cc's. The average Chevy piston has 7 cc's worth of valve relief and we know the chambers are 76 cc's. This computes to 8.34:1 static compression ratio. I'll take a guess that the cam has an intake closing point of 29 degrees ABDC. This computes to a dynamic compression ratio of 7.583:1. Normally, you would shoot for a DCR of 8.00 to 8.25 if you had a tight (0.035" to 0.040") squish in the motor, so there may be a little left on the table with this motor. The problem is, we are not sure of the deck height. I'm assuming 0.040" and with another 0.040" in the gasket, that puts the squish at 0.080", not optimum for more compression with pump gas.

If you left everything else the same and swapped to 67 cc heads, the static compression ratio would be 9.07:1 and the dynamic compression ratio would be 8.238:1. Now, again, if the squish was tight on the motor (which we don't know at this point, this DCR would be perfect for optimum performance from the motor on pump gas.

I don't think you can make a decision about the heads until you pull your heads off and measure the deck height. If the motor was built with zero deck (highly unlikely), then you are "in like Flynn". You could also use a thinner head gasket with the 67 chambers to tighten up the squish, but you wouldn't be able to go much thinner or the DCR would go out of sight and you'd start detonating the motor on pump gas in my opinion.