[PeteKz]

Bob, maybe someone here has done that and can give you exact numbers, however, even then, you should measure the minimum clearance between your pistons and the heads, at the edges and wherever the piston dome comes closest to the inside of the head. In 3.0 and 3.2 engines, these are already pretty close, so you are very limited in how much compression you can get by flycutting the heads. I'm not sure about 3.6 964 engines. Measure yours, then you will know. Do not go below .030"/.75mm minimum clearance. Also check the valve to piston clearance when at overlap with the cam you want to run. Do not go below 1mm/.040" at the minimum valve clearance point. More is better here, and the general consensus is that .060"/1.5mm gives a better margin of safety if you over-rev the engine.

Other possible option: If you have any shims between the cylinders and the case, you can remove those to increase the compression slightly.

To get a significant bump in CR you almost always have to use new pistons with different domes.

I also recommend you talk to William Knight, as he specs and builds racing engines. "Knightrace" here on the forum.