Head would be at its limit already without going to spark plug inserts - 40cc is the numbers from the des hamil pinto book with a big skim and deshrouded valves.

The CR's I got, with 0.75mm piston head clearance - probably use a 1mm HG although it won't matter too much as I can take that into account when skimming pistons/ block.

If I skim the pistons to the following crown / ring heights I get the following CR - so from 8.3mm standard

8mm = ~8.7
7mm = ~9.3
6mm = ~9.9
5mm = ~10.5
4mm = ~11.1

So if taking 4mm or so off the piston crown is safe, then this looks like a winner :t-up:


Thanks for your help, been looking for those figures for ages.