In any case, the position of the piston ring will have only a very slight affect on the C, since there really isn't *that* much volume between the pistons and the cylinder walls in the first place. might be in danger of dropping past significant digits in terms of the accuracy of the more directly relevant measurements (such as the combustion chamber volume).

.028" may be a tiny bit closer, you might want to aim at .032. When the motor heats up, the rods stretch. And when the motor is revved up, they stretch a little more. Don't want them to touch the head if you reav it up a little too high.

Zeroing the piston height isn't integral to getting an omtimal quench height, but an accurate measurement of piston deck height is needed before you know what thickness of HG to get. If you are wanting to set it to a fine degree of accuracy, consider a copper HG, you can specify a precise thickness and it won't compress. There are several heights of the standard compressible HG's, but then you have to reverse engineere the deck height to match, which isn't as easy as jsut picking the HG thickness from a wider range of options. Cometic also makes MLS HG's too, AFAIK. Not sure if the ones I've heard about were special order or not.

With good quench, you can run higher CR with lwoer octane gas, however, I'm not enough of a motor building genius to be able to suggest what CR/quench/octane ratings might go together properly. I'm guessing that it might be worthwhile making a motor that can run easily on regular gas these days. My PV needs the premium, $0.20 (at least) more a gallon that you have to pay every single fill up.
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'63 PV544 rat rod, '93 Classic #1141 245 +t