[Alan Roehrich]

A good quality coating on the piston skirt will make the hone finish on the cylinder wall last longer. I've seen that myself, and my findings were duplicated by several others, including the Morgan brothers who worked with Reher and Morrison.

An oil shedding coating on the bottom might prevent oil from clinging to the piston, allowing more oil to return to the oil pan.

A thermal barrier coating on the top is most likely illegal. But it will allow for a tighter piston to wall clearance, and will reflect the heat back into the chamber.