Once reserved for high-end aerospace and military applications, high-tech coatings have percolated down into racing and in recent years have even become available to mainstream hot rodders.

So just what are engine coatings, anyway? Basically, they are an entire family of chemical surface treatments applied to various engine components. Depending on the particular coating and the desired end result, the object is to prevent the migration of heat, radiate heat, reduce friction, or shed oil. Most coatings fall into one of four broad functional categories: antifriction lubricants (lubricity coatings), thermal-barrier coatings, thermal dispersants, and oil shedders. Some coatings may fall into more than one category. Detailed composition info is a closely held secret among various competitive coating outfits, so we'll concentrate on the claimed benefits in typical applications rather than get into detailed, high-end metallurgical metaphysics.

Lubricity or antifriction coatings consist primarily of dry-film or solid-film lubricants that reduce friction, galling, and seizing. In some instances, this category can also help disperse heat. These coatings typically contain molybdenum disulfide or tungsten disulfide. The application method and binder technology are critical in getting the coating to stick to the metal surface in long-term use.

In the engine's bottom end, dry-film lubricants are usually applied to piston skirts, engine bearings, and the main and rod journals. On the top side, dry-film lubricants are sometimes applied to timing chain sets, valve stems, rocker arms, pushrods, lifters, valvesprings, and cam lobes. Additionaly, dry-film lubricants can be applied onto manual transmission gears and ring and pinion gear sets. Under heavy loads, moly-based dry-film lubricants can actually hold oil on their surfaces, enhancing the integrity of the oil film between the metal parts. These same lubricants can delay metal-to-metal contact if oil pressure is lost. Although some claim that by reducing friction, lubricity coatings should offer some power gains, normally an engine's journals and bearing surfaces are separated by the oil film and never come into contact, so it's hard to see how coating the bearings would add any power under standard operating conditions. Therefore, the main advantage is really as an insurance policy, enhancing longevity and providing emergency protection if something goes wrong.

Lubricity coatings also lower a part's temperature. Applied to upper-end parts like valvesprings, they can greatly extend their fatigue lives. Some builders claim a 15- to 30-degree oil-temperature drop, which could permit using thinner oils without compromising parts longevity. Thinner oils offer less drag, which may translate into increased power.

In theory, heat management offers great potential for improving an engine's power output. Often, ceramic-based thermal-barrier coatings (TBCs) are used to reduce heat migration, reflecting heat rather than absorbing it. They may be applied to piston-top surfaces and top ring grooves, combustion chambers, valve heads and faces.

When applied to piston tops, TBCs reflect heat back into the combustion chamber. The additional heat translates into more energy to push the pistons down. To the extent coating the piston tops makes the top surface smoother and minimizes the development of local hot spots on the pistons' surfaces, TBCs may decrease detonation potential. On the other hand, TBCs may prevent heat from dissipating down into the pistons and rings, through the cylinder wall, and into the water jacket; this may actually increase detonation potential. The tilt point is related to whether the engine will be subjected to heat over a long period (as in an endurance motor) or in short bursts (like a drag-race).

Setting up a thermal barrier in the combustion chamber also helps the chamber retain heat for more power potential. Again, assuming detonation does not become a problem, this can increase combustion while lowering engine-coolant temperatures. Aluminum heads, which are said to reject heat quicker than traditional cast iron, may see particular benefits from TBCs. Barriers can also be applied to valve heads to keep them cooler.

There is also a high heat I.D. coating known as TLHB. This coating is applied to the inside of the exhaust ports to keep the hot exhaust gases inside the port. This coating is useful in turbocharged applications where it will help spool up the turbocharger reducing turbo lag with higher exhaust gas velocity. This coating also keep cyliner head temperature down preventing pre-detonation. On the inside of chrome pipes it will also prevent bluing of the chrome.

Usually based on PTFE (Teflon) or similar fluoropolymers, oil shedders, as their name implies, help a part shed oil to improve crankshaft windage and oil return. They are usually applied to the undersides of pistons, connecting rods, crank counterweights, windage trays, and the insides of oil pans, timing covers, and valve covers-anyplace oil isn't needed. Shedders may improve overall high-rpm engine lubrication while reducing oil temperature and can also help reduce varnish, sludge buildup, and corrosion. To the extent shedding oil may cut drag on rotating parts, power benefits are also claimed.

These are the opposite of heat barriers: They radiate or disperse heat. As previously stated, keeping heat in the chamber is good provided you don't get into detonation. But if you do have a detonation problem, a dispersant could be in order. Many thermal dispersants are dual-category products. Besides their antifriction properties, dry-film lubricants often disperse heat (their use on valvesprings would be one example of dual-category use). Other, proprietary, thermal dispersants take the place of traditional black paint and are sometimes applied to brakes, intake manifolds, cylinder heads, oil pans, radiators, and intercoolers.