Rick Carter

Here is a good place to start.

Dynamic Compression Ratio Calculator

drnick

im sure jim bailey mentioned that this has been done already in australia and that the engine had trouble running on pump gas.

Jim bailey - 928 International

The GTS has problems with detonation same heads (But with extra cooling on the exhaust port )....And yes One customer in Australia tried the 85-86 USA short block with S-4 heads it was NOT HAPPY neither was he ! Just the thought of taking out the head studs from the 85-86 block would deter me from wanting to try this, I would only use the 87 > head bolts. You could get away with the high compression by running race fuel but that gets expensive as well.