There are two types of coatings; Thermal Barrier, and Dry Film Lubricatant. I have run both in more than one engine...
Thermal Barrier rocks! Had an air cooled 4 cylinder and it was runnning HOT. Pinging at 10 to 1. I Thermal Barrier Coated the pistons, combustion chaimber of the heads, exhaust port runners, and headers. My headers are 10 years old, and have no runs. Oil temp fell about 100 degrees, and I went up to 13 to 1 compression useing pump gas, but with water injection. (Edelbrock Varajection) The coatings can handle up to 1900 degrees without transfering heat. This increases thermal efficiance because the heat goes into expanding the cylinder, not heating the block.
Dry film lube is a coating for moving parts. Hard grinding wears it away. On berrings, it is "insurance" against sudden loss of oil pressure. While it will wear away from those surfaces in normal use, it takes half the life of the engine to do so... No benifit unless you loose oil...
On rocker arm surfaces, it wears away instantly. On cam and lifters, it adds a small ammount of time to cam break in, but reduces chances of flattening a lobe on startup.
The sweet spot for this is if you have a splash lubricated surface with light pressure. Examples are doubble valve springs with a dampener, or timing chain. Big gains can be had here. We measured it by spinning an engine with no valve train and seeing how much voltage it took to spin at 700 RPM. It was about 20 percent less. (Not sure how that translates in HP) The big benifit is in sprin/timing chain life. A race engine has 6 seasons on one timing chain with no strech. He used to be lucky to mak one season. He is also getting a full season out of the valve springs. The are good at that time, but the valves are not, so he replaces valves, seats, guides, and springs anyway. (Sponsered dragster, the bastard)
Of course, all of this depends on the shop. I live in Houston, and PolyDyne has been doing this for top racers a long time.
There are coating that will last and coatings that won't. If they can't tell you what there putting on and how they're doing it don't try it. Best thermal barrier is Yitrium stabalized Zerconium Oxide. It grow columner so the yitrium is used to keep the columns from splitting. This is applied by plasma spraying, e-beam evaporating or sputtering depending on how stokiometric you need the oxide. New jet turbine sections are carbon fiber composite blades with Zirconium oxide coatings.
Oh yeah, why is it better? Keeps heat from transferring to the oil and water. Gas temperatures rise so does pressure. More power but the exhaust valves take a beating so use inconel.
i run an 11-1 motor in my boat and can get by on pump gas and octane booster w 34 deg timing.But try to run 100 and 38deg also do this with a 100 hp nos.
As for alm heads i think iron is beter for a boat since a boat motor runs cooler and needs heat in the combustion chamber
Oh yeah, why is it better? Keeps heat from transferring to the oil and water. Gas temperatures rise so does pressure. More power but the exhaust valves take a beating so use inconel. I used stainless, but I had the heads squarted with the valves in. A clean up cut finished them off. The coating on the surface of both, and the back side and a bit of the shaft of the exhaust prevented a lot of the heat transfer, and still allowed the exhaust valve to bleed off heat via the valve seat, guides, and the oil bath under the spring. But yes they are stressed, so don't use the cheapies!
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