Agree, the anti-friction coatings must do something, because almost all the OE's use them on piston skirts. They do it for mileage and emissions. Coating allows tighter piston to wall clearance which means fewer hydrocarbon emissions. Anti-friction results in less heat and more HP. The real question which nobody can put a number on, including the coating manufacturers and sellers, is how much HP gain. Is it 2 HP on a 1000 HP engine?, 8 HP? They never want to put a real number on it. Certainly isn't anywhere near 50 HP or as I said, sanctioning bodies would be all over it. We run "hard anodized" pistons in our car. That could be considered a coating, I guess. We do it to provide a greater margin of error in our tuning. The soft aluminum piston is shielded from melting a fraction of a second longer with the coating than without. Think of it as the difference between a regular fuse and a "slow blow" fuse. So in a sense it makes more HP by remaining a piston longer than a glob of melted aluminum. Coatings have their place in an engine, but there are many more cost effective places to spend $$$ first.
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