Actual piston sizes are 3.631" and cylinder sizes are 3.641. Not really bad. BUT, the end ring gap is .030. Keeping in mind that these are .015" over stock on pistons and bores. These are seacross pistons, don't know if they are cast or forged, but cast clearances to bore S/B cir. .005 and forged to bore S/B cir.008. It looks to me that the bore is a shad large for these pistons and rings look to be standard size on a .015 over piston.