I've got the motor running with the new cam, everything looks and sounds real good. Awesome torque and great HP.

My question is how do I know how much octane I need to run? Here's some specs:
- 12.15:1 Static
- 8.1:1 Dynamic
- 302* Camshaft, 114LDA, 1* Advance
- Old-style Iron 64cc combustion chambers
- .045" Quench, 0.100" dome pistons
- 270PSI Cranking pressure

The dynamic compression tells me to run 92-98 octane fuel. However, the cylinder pressure tells me to go to 110 or so. Currently, I'm running a 50/50 mix, which is about 100-102 octane (and I retard the timing by 4*). The problem is that I don't think I'll be able to hear it ping or detonate if the octane is too low. What do you guys think? Ideas? Any other methods to use when determining octane requirements?

Wow, someone is probably going to come along and tell me I'm crazy, but some part of that doesn't seem right to me. I've got a 355 that I'm freshening up right now, and its got the larger domes, .240" without looking again. I know they're 11cc's. I have a little more quench at .054, but a much smaller cam. My static is about the same as yours at 12.29, but my dynamic comes out at 9.4. I could see why your dynamic is where it is, with your larger cam, and wider lsa, but it just doesn's seem to add up to me with the cranking compression. Cranking compression was between 235-240 all around on my motor, and it got by on a mix that came out to 95 octane, that was before the aluminum heads were going on. If you want to try something less, just do it gradually, leave room in the tank incase you need to add more good stuff, and keep an eye on your plugs. This time around I plan on trying some of the kemco 130 I've heard so much about.

I know the cranking compression seems fishy, I've racked my brain about it a whole bunch. I've re-degreed the cam, and it's in there correctly.

With my old cam (296* duration), it was 240 PSI. Weird, huh? But it does run darn good though...

I agree that this does not seem right. My 498 cu-in has 14.58:1 compression ratio and produces around 260 psi. I have a .660 / .660 @ 264/272 @.50 solid roller (ultradyne) and run VP C14 race fuel. I tried 112 octane and it is boarder line depending on the spark plugs I use.

Tino

I dunno. I posted about this a while back and nobody was able to give me a straight answer except for UDHarold.