Octane Ratings

[73stinger]

Is there a way to calculate what octane gas I need, by the engine compression ratio?

Thanks

 

[Stallion]

What CR are you running? There is a standard. But the way I understand, CR can be somewhat misleading. What really matters is your cylindric pressure. And that is the duration and lift of your cam, I'm sure.

 

[73stinger]

My L-48 is listed @ 8.5:1 compression. But how high could i go on regular gas?

 

[Stallion]

Oh I think you are fine with regular. L82s (at least in '78) are rated at 8.9:1 CR, and they run regular. You aren't getting any pinging are you? I don't think you would detonate with regular.

 

[Stallion]

Oh I see what you mean. I think you could go low 9s to run regular. Then you might to start need the higher octane. It depends on your cam, I think, as well too. But if you change your pistons out and that's all to get a higher CR, then I think you can get low 9s with regular. I would wait for a 2nd opinion on that one though, because I'm not 100% sure.