I read an article in a Mopar magazine a while back, there seemed to be quite a few high tech coatings out there. As I recall coating the inside of the piston helped keep temps in the combustion chamber and out the pipes, and less heat transfer to the crankcase/oil. But perhaps the whole piston was coated.
I'm not sure how it would work, coating the head and keeping more heat in, in hopes of blowing it out the pipes. Does seem like you would want the head to transfer heat away...? But I don't know. Exhaust ports and pipes make sense. Wrapping the pipes to keep heat in and out the exit has been used for some time now...so coating the pipes, inside or out makes sense.
Not sure if you would want the barrels to do anything but radiate the heat away...but again not sure. To my mind the piston, exhaust port and pipes would give the greatest gains. Wonder what exhaust temps coming out the end of the pipe/muffler would be?