when talking about piston to wall clearance, is the measurement from the piston itself or is it the rings everyone is talking about. i.e. having a piston clearance of .0035", etc. or does everyone get pistons custom made to that size? or is that already factored in by the company so when you get pistons for a 81.5mm bore they already have the .00whatever taken out of them?
sorry did a search but could find much to explain it

 

you buy your pistons for whatever bore you want, then the machine shop bores and/or hones the sleeves to the proper size to achieve the P2W clearance that you want. Some go about this backwards and measure the cylinder, figure out what it will take to clean them up and then buy the piston of the proper diameter....it really kinda depends on your situation. If you are buying a sleeved block then you have the option to make it whatever you want. If you are reusing a block then you are limited to what the bore already is and what it will take to clean the cylinders up, and the max amount power the stock sleeves will handle


P2W is the cylinder diameter minus the piston diameter divided by 2, since there is 2 P2W gaps, one on each side of the piston

ring gap is just that. it is the gap in between the ends of the rings

 

cool, couldnt of asked for a clearer answer