When I started building them, they were intended for a .030"-over 292, with flat top pistons. Accepted theory then was, as Y-Block compression is so hard to achieve, an upper limit was never considered.

I now find myself with 318" displacement, and pop-up pistons. When originally chamber-matching the heads, I estimated final volume at 68cc's. With block zero decked, calculated CR is 9.5:1. However, due to abject laziness & wrongheaded assumptions (don't ask), I have ended up with 66.2 cc (smallest chamber). If CR variations due to volume are indeed linear (?), that comes out to 9.8:1. CR.

So, do I bite the bullet and disassemble/grind/clean & CC the heads again multiple times in trial & error attempts to achieve my original target volume (this IS a mild street motor), or will other variables with this particular application that might allow a higher CR (limited breathing, tight piston-head clearance, above average ignition curve/limit control, mixture effects of piston domes, etc.) give me enough leeway? (I would almost rather drag around a case of octane booster, that have to start over again on the heads). Of course, if more chamber grinding IS absolutely needed, better now than after the engine is installed.

6 VOLTS/POS. GRD. NW INDIANA