[IXjamesXI]

Yeah, E85 is a can of worms that I have no interest in opening. Maybe one day when I get turbo fever I will perhaps look at it in a different way.

Yes, dynamic compression ratio is an interesting concept and learning about its existence is what prompted me to start thinking about my engine in a different way. A static ratio I guess does not take into account what effect the rest of the engine geometry, including the cams, has on the actual compression and pressure.. I learned that low overlap cams make more dynamic ratio than higher overlap ones. I still have a lot to learn, and I don't know if you can really trust that figure to make comparisons between engines, but here are some numbers that I have been looking at..

A 964 in stock trim has a DCR of about 8.1:1 to 8.2:1. Now of course these engines have twin plug and knock control. And this assumes a "real" static CR of about 10.7:1

My lowly SC in original form had a calculated DCR of about 7.38:1, single plug, stock.

The engine I am building now, including a custom cam which I plan to get from camgrinder, would have a DCR of 7.4:1 at a static compression of 10:1, or a DCR of about 7.6:1 at a static compression of 10.5:1.

I have read on the internet some guidelines for DCR, but I think they really applied to V-8's and not our oddball hemi head detonation prone engines, so I am hesitant to apply those rules of thumb. My hunch, based on comparing the SC and the 964 above, would be that a DCR between 7.4 - 8.0 would be "safe" but that's just because its the range between two known combinations that work.