[hgerhardt]

My 428 with Ross flat tops and zero-decked block and 72cc E-heads is 11.4:1 and is happy with 91 octane. Cam is 248/254 @.050 and 114 LSA.

So much of this is dependent on cam timing. It's the dynamic CR that's important, not static. Dynamic CR is determined from when the intake closes on the compression stroke. The later the intake closes, the less dyn CR you'll have.

An example: this engine with the same cam originally had 87cc E-heads (9.7:1-ish) and I accidentally figured out that it ran better on 87 octane than 91. With the 72cc heads, throttle response is sharper, and I picked up around 1/2 sec in 1/4 mile. Much happier motor!