The exhaust is able to exit the pipe much quicker because it isn't radiating thru the exhaust walls, In return the air is able to keep a smooth flow out of the pipe end. This helps the exhaust gas exit the exhaust port without much pressure building up in the pipe. Hope this helps, as i'm not the best at trying to find the right words for explaining things in detail.
I do agree that it won't be very beneficial when it comes to small glow engines. But yes the bigger gas engines may work well. As far as cowl temps it will reduce the heat. These particular ceramics reduce normal under hood temps by 400 degrees F. (this is car and truck)
I do many piston coatings also, I think I will give that a shot. This mainly is a friction reducer for pistons, Crankshafts...
They have brought them back Jim. I don't know how these compare to the coating of the 70's but... I do many race engines and most of these guys usually bring the vehicle in and use a leaf blower to keep them cool when they shut down, the ones I have coated don't produce near the heat as others. I don't have actual numbers unfortunately but when standing next to them you can put your hands very close to pipes as where there isn't a chance of it on the standard set ups.