Originally Posted by hcompton
I get 10.7:1 which can work on the street with alum heads. With a .041 head gasket.
That would be a lot to ask for from cast iron heads. Now with a giant cam and good tune with good weather conditions maybe 93 will work but hot engine on a hot day may knock. Best to stay in the 10:1 range for most cast iron applications. Larger cam can help but with smaller cam regular flat tops would be a better bet also cheaper. Depends on the end goal. All out racing more is better as long as you got the fuel to support it.
Can you get e85 in your area? Not in mine but works good for high compression engines when carbs are tuned for it.
The engine is already built and running with the .125" dome pistons. Those unfortunately won't change as well as the fact they are .025" in the hole. If I run a .041" gasket my quench is trash. This is why I ran the .015" shim gasket to get a .040" quench. Also, with the combination I have currently it is 10.2:1 CR and still detonates because I can't run full timing because of the larger chamber, thus wanting the smaller more efficient chamber. I have easy access to all kinds of fuels where I'm at so if i have to run 100 all day everyday, that will suck but can be done as this is going to be a drift car that isn't driven often enough. Plus if I were to run the aluminum SHP heads, that will be like dropping my compression a full point so I'll be roughly 10.4:1 which isn't too different from where I'm at not but with a more efficient chamber and fast burn rate. I just need to make sure the dome will clear the "heart" shape of the chamber or the pistons will need to be clearanced.