What's the most compression a naturally aspirated 331 can handle on 91 octane pump gas? I currently have a 10:5 C/R with my AFR 185's (61cc). If I ran the 58cc heads, what would my C/R end up being & would I still be able to use the pump gas for my weekend driver?
The 58cc would bump you up to around 10.8:1
You would still be ok driving with premium. I would run some race gas if you planned on spraying nitrous though...
I guess you see that Thumper added the rest of the equation - you can run about as much compression as you like if you retard the timing enough. But if you want to run a reasonable amount of timing, something around 11:1 is likely to be where you'll start running into the limit. It also depends on geography - gasoline formulations are not the same every where in the country; and it varies seasonally - the warmer weather will be likely to cause detonation where it wouldn't detonate in the dead of winter; gasoline formulations are different seasonally too. It's those kinds of differences that allow for why some folks get away with a higher number than others. Quench also has a big impact on detonation - another potential variable from engine to engine.