some items I want to point out. Starting with the first post, the coating does not absorb heat, in fact this is the beauty of the coating. It is thermodynamically impossible for something to absorb heat without releasing it or doing work on the system.
I have to seriously disagree with any statement that a coating on the top of the piston will increase the potential for detonation. Detonation is casuse by 1 of 2 things, either extremely high pressures, or high temperatures on the combustion chamber's walls PRIOR to combustion.
As said before, hot spots on a piston can be a cause of detonation, the coating insulates the piston allowing the piston to run cooler, but in order to do so, it must be assumed that the coating does not absorb heat as efficiently as the metal piston. Thus, after the exhaust gases have exited the chamber the top of a coated piston will be cooler than the top of an uncoated piston.
Since heat is not absorbed into the piston, this means that the gasses inside the chamber will be hotter, but ONLY AFTER the spark plug has lit and the combustion process has begun, thus, it is not Pre-ignition. Those hot (or hotter) gasses are expelled on the exhaust stroke.
So why would they say that chances for detonation are INCREASED? I'll tell you why, if heat cannot be absorbed into the piston, the gas temperatures will go up. If the gas temperatures go up, the heat tries to find another way out (before it is expelled on the exhaust stroke). It does so in 2 different ways:
1. Less thermal loss (Q-out) means more work done (W-out).
2. Since the heat isn't absorbed into the piston, it absorbs into other parts, say the cylinder walls, the head, the valves, oh, and most importantly the spark plugs.
You should all know by now that spark plugs come in heat ratings. Hot plugs and Cold plugs. In boosted, nitrous, and racing applications, the plugs will get so hot they'll become glow plugs and detonation is a problem, well, same goes in this situation, the cylinder temperatures are higher and the plugs are getting hotter.
Don't quote me on this, but I'm almost positive that if you coat your pistons, AND you change to a colder plug (say a 7), you'll greatly DECREASE the chances of detonation.