Quote:
Originally Posted by 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.
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the piston to head clearance is .050'' at the step and .070'' on the dome with no shims. These cylinders take an 0 ring, and I guess you can include shims if needed in your build. My thought was to take .010'' off the cylinder to get the piston to head numbers a little better and .020'' out of the head to bring up compression. Problem with shortening the cylinder is you are reducing the CR. Valve to piston has been satisfied even with making the new mods. Chain slack issue is my present concern. Thanks, Bob