I am about to embark on another (doubtless expensive) exciting adventure with the Porker. This time an engine...
I have sourced a 924 Turbo head, and I plan to add it to another block (When I can find one) and add a fast road cam. The ultimate in 924 N/A is the plan with second hand parts and no budget...
Problem is that will drop the CR from a healthy 9.5:1 to around 7.5:1. Not much cop. So to fix that I plan to deck the block to get it back to standard CR. This may seem a little drastic, but as the N/A head is totally flat and the Combustion chamber is the top of the bore its not as bad as it sounds. The turbo head has a combustion chamber in the head as well as massive valves ports and so on.
The question is this, bearing in mind I have EFI and Wasted spark running, should I go for the minimum skim of 3.6mm to get back to 9.5:1 or should I squeeze the tolerances and go for a bit more CR? I can maybe get away with 10:1 or 10.5:1 if I'm lucky. Would it be worth the risk or close tolernaces? The engine would probalby still be non-interferance (Just) but that is the tolerance I am playing with. I really need to get hold of both a block and the head to find out for sure.
Clearly by decking the block so far the combustion chamber dynamics are going to be bunk anyway also the turbo head normally runs with turbo pistons which are an off shape too.
the final plan is to codge up ITBs from bike throttles with really long runners if possible and chop up a 944 manifold to make a 4-2-1 exhaust. But that will probably never happen...
Oh, and when i had hair, i had rather a lot of it 
) I dont see any reason to stick to a 9.5 c/r since you've got efi and petrol is good these days. I might not go straight to 11, but stick at 10.5 - that way if you need to skim the head, you've still got a bit of leeway.