safe compression ratio with 91 octane pump gas

[Rhombeus50]

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?

 

[Stangoritah]

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...

 

[charged9250]

So what is the most compression you can run with 91-92 octane?

 

[thumper460]

I'm at 10.9:1 on ported E7 heads on 93 !! Total ign timing at 38* no ping here!! and the alum heads will usually take more...

Just me.........................

Thumper

 

[charged9250]

Thats sweet..I'd like to build a 393 with 10 or 11:1 CR and run 92 octane. Anyone else got info?

 

[Michael Yount]

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.