The purpose of cam grinding is to maintain close to the same clearance when hot and cold. With proper piston design, you would have between .001 and .002 thou. clearance when cold, for instance. When heated up, the piston expands along the length of the wrist pin and the clearance perpendicular to the pin stays the same. I think part of the reason the motor has more power at start up is the viscosity of the oil is higher making for a better piston and ring seal.