I read an S.A.E. paper written by a Japanese auto maker who studied polishing the combustion chamber and piston tops in a production based engine. They also studied various commercially available reflective ceramic coatings that are available. There conclusions were that polishing all of the components that "see flame" in an engine led to increases in performance and fuel economy on the order of 1 - 2%. Interestingly, none of the high temp coatings showed any improvements in efficiency whatsoever. Their conclusion was that although polishing helped, it was not economically feasible in a production engine.
Or so they told the rest of the world.
I polish my chambers and piston tops in every racing six I build. Hey, in a 500 HP engine 2% is an extra 10 HP for a few hours of work and no money. I'll take it.
