Re: Finned and Edmunds style H/C Heads

Posted by Eric Boyle On 2008/1/1 20:18:19

You could go 9:1 if you make sure the timing's absolutely correct with 87 octane fuel. Keep in mind when considering compression ratio's that all fuel is going to have Ethanol in it, because the old oxygenation additive is "bad" for the environment. Ethanol is a good oxygenator, and is also hard on fuel systems set up for the old fuel. A positive side effect of the Ethanol, even though it's not much unless you're getting E-85, is that alcohol burns cooler than gasoline, so it's easier to raise your compression ratio. It also doesn't make as much power as gasoline, so it's all give and take anyway you look at it.

Bottom line is, if you happen to run 9:1 c/r, keep an eye on pinging in the engine. I highly doubt you'd have a problem though. I'd personally use 89 or higher with a 9:1 c/r.

So in other words, 8.7:1 is probably the best bet. Me, I'm going to go with 8:1, or maybe even 7.5:1, since I'll be using turbos.