However, I would be interested in knowing what piston mfg wouldn't base their piston size on a nominal bore size ie. stock plus 0.030". You would think that they would vary the piston diameter to attain the correct clearance and not the bore size.
Manufacturing tolerances vary. They don't mic every piston that comes out of the shop and a cursory inspection and a go no go gauge and it's the box. A well machined and blueprinted bottom end makes all the difference. It's also why two engines from the same manufacturer make different HP. It's all about tolerance stacking. Forging and casting dies wear and heat with use. Was the piston the first on the die of that day or the last? Was it the last piston ever forged or the last before it was replaced? No way to know until you mic 'em out.
