High-tech coatings for engine and driveline parts have been around for decades, but they have had a voodoo mystique about them that scares off the typical hot rodder. It’s kind of like the stigma nitrous had 15 years ago. And as with nitrous, the uninformed enthusiast still believes the old stories associated with internal engine coatings. Early, poor-quality coatings sometimes deserved their reputation of poor durability and ineffectiveness, but when you consider that most of the top Winston Cup and Top Fuel teams (and even a few O.E.M.s) use several types of coatings in their engines today, we think they’ve proven themselves. Hot rodders owe it to themselves to take a look at what’s available.
There are three main types of coatings, and their names are self explanatory. Thermal-barrier coatings hold heat in, heat-dissipating coatings let heat out, and low-friction coatings remove power-robbing and heat-inducing friction. There are also a few coatings that are purely cosmetic—they look good, are very durable and clean up easily. Virtually every part on a car can be coated, from the suspension to the pistons. We’ll start with thermal-barrier coatings (TBC).
Heat makes power. The more heat you can generate, the more power an engine will make. Unfortunately, the internal combustion engine is terribly inefficient when it comes to managing heat, using only about 20 percent of the heat energy created by the combustion process. Most of the energy escapes through the exhaust system or is absorbed into the engine and removed by the cooling system. Obviously, you can’t eliminate the exhaust system, and the cooling system is mandatory to keep the internal parts from melting or coming apart due to extreme heat levels. The only thing we can do to make an optimized engine more efficient is to more effectively contain and manage the heat that’s made when combustion occurs. That’s the purpose of thermal-barrier coatings.
The most commonly used TBC is a ceramic-based material that’s applied to the top of the piston and to the combustion chamber and valve faces in the cylinder head. The TBC holds more heat in the chamber, instead of letting it dissipate through the piston, valves and head (where it is then absorbed by the cooling system). This theoretically increases cylinder pressure and pushes harder on the piston, making more power. The TBC also protects the aluminum piston from the intense heat, so the air/fuel mixture can be leaned slightly for maximum power without burning through the piston. And, since the amount of heat radiated into the rest of the engine is reduced (since it’s contained in the chamber), the operating and oil temperatures of the engine come down. This is also beneficial to the piston rings, improving their radial tension and sealing ability. TBCs are also used on intake and exhaust ports and headers to improve scavenging and lower the underhood temperature. They are also used on the underside of an intake manifold to keep hot oil from elevating the intake charge temperature.
The three key players in the coating game are High Performance Coatings (HPC), Polymer Dynamics (Poly-Dyn, for short) and Swain Tech Coatings. Much of each company’s information is proprietary, so they wouldn’t tell us exactly how the coatings are applied, but they’re much more than mere paints. A two- or three-part process is used for TBCs, and the coatings normally go on with a thickness of .002 to .004 inch, so very little compensation needs to be done during the machining process—unless of course the pistons are at zero-deck before coating. The coating material is permanently bonded to the part, so the old problems of flaking have been eliminated.
Low-friction coatings, also known as dry-film lubricants, are split into two types: self-lubricating and oil-shedding. The self-lubricating type of dry film is applied to piston skirts, valvesprings, camshaft lobes, engine bearings, wristpins, valve stems and oil and fuel pumps—just to name the engine-related parts. Most of these coatings are polymers, although each company has a slightly different combination of materials. Swain Tech, for example, uses a moly-tungsten-disulfide material in high-load-bearing applications, such as on cams, valvesprings and wristpins. These materials hold oil on the surface of the part and have a very low coefficient of friction. Applied to a piston, the dry film reduces piston-to-cylinder-bore friction, which also reduces bore wear. Swain Tech is experimenting with cylinder-bore coatings as well, but some feel that coatings take away the all-important crosshatch and, therefore, ring seal.
Another application where a self-lubricating dry-film coating shines is on valvesprings. Tests have shown that uncoated valvesprings can run 30 degrees hotter than the engine oil, while coatings on the springs bring the temperature down about 20 degrees, which can dramatically increase the life of the spring, allowing it to maintain tension longer. The self-lubricating dry-film coatings are especially helpful in situations where a part is momentarily starved of oil. Dry-film coatings are typically applied less than .001 inch thick, so there’s usually no need to compensate for them during machining.
The oil-shedding type of dry film is used on connecting rods and crankshaft counterweights to reduce windage as well as in engine-block lifter valleys and oil pans to aid in oil drainback. This polymer acts like the Teflon® or nonstick coating in a cooking pan: It beads up oil and won’t allow it to stick. The third type of coating is for heat dissipation. Swain Tech’s heat-dissipating coating is a black body emitter, using high-emissivity materials such as copper oxides, vanadium and some ceramics that radiate heat off of a surface. Applied to the exterior surfaces of the engine block, the intake manifold, the brake calipers and about a hundred other parts, these coatings get heat out of a part. They aren’t pretty (unless you like an all-black engine), but they’re functional and very durable.
There are other coatings available that have minimal effects on heat and friction and instead are purely for cosmetics. These coatings are typically applied to headers when a true thermal barrier is not needed, as they are impervious to oil and chemicals and won’t discolor or flake off with high heat, which is a problem with chrome and high-temp paint. They still reduce underhood heat a little bit, but not to the level of a TBC. Some of the better cosmetic coatings also protect the header from thermal fatigue, which is the real header killer. Cosmetic coatings are also commonly applied to intake manifolds, suspension parts and other parts that are otherwise hard to keep clean or subject to corrosion.
Theoretically, every internal engine part can benefit from some type of coating, but the largest benefits are realized by treating the pistons, combustion chambers, valves, exhaust ports, headers and valvesprings. For the hot rodder on a budget, these are the areas that will give the most bang for the buck from both horsepower and durability standpoints.
At this point, you’re probably wondering how much this all will cost, and what it’s worth. Well, price is relative to the value you place on durability and that last little bit of ultimate power. To fully coat an engine inside and out will run you around $1000 and may provide a horsepower increase of about two to five percent. But horsepower isn’t really what coatings are all about. Rather, long-term durability is the key. There are three reasons for engine coatings: to reduce friction, to improve thermal efficiency and to improve the durability of the engine. None of these three provide much in the way of immediate, seat-of-the-pants benefits. But if the motor goes way lean at the big end, chances are you’ll burn a piston or two and maybe even take out something bigger. And temporary oil starvation, even for a second, will create a box of broken parts faster than you can say “What the…?”
An engine treated with quality coatings has a much better chance of coming through the catastrophe alive, and chances are the major parts can be used again, saving significant money at rebuild time. Also, other than the cost, there are no drawbacks or compromises to coatings. Ask yourself how much your engine is worth and how badly you crave that last 10 horsepower, and then decide if coatings are for you.
