Courtesy of Comp Cams
Almost thirty years ago, my initial exposure to aerospace coatings in racing was in the application of an aluminum oxide plasma spray applied to clutch friction surfaces. The results were so outstanding that it quickly appeared viable to apply the same material to the crowns of pistons, largely to improve power. In this case, the results were disastrous, enabling small flakes of aluminum oxide (at a Rockwell hardness of about 70C) to wipe out the rings and score cylinder walls. However, before the damage, it became apparent that the anticipated power gain had occurred, albeit with problematic side effects. Essentially, the difficulty lay in maintaining proper bond strength, largely because the technology had not yet embraced specific automotive requirements.
Shortly thereafter, I met and came to know another person with a strong desire to explore the potential benefits of thermal coatings. He had a broader vision of the notion that included the application of materials for friction reduction and corrosion prevention. Also on his mental landscape were ways to improve valve spring life through friction reduction and temperature control. His name was Leonard Warren. But Leonard wasn't the first to contemplate the transition of aerospace coatings techniques into the motorsports environment. VHT paints had been around for a time (largely applicable to exhaust headers) and Smokey had previously showed me dyno results from some "heat paint" he'd been using on the underside of piston crowns. I'd also had the pleasure of meeting and working with Jeff Holm, founder of High Performance Coatings, in particular with respect to his ceramic coatings for headers. While all this technology had begun to evolve in the high performance sector, it was quickly gaining a foothold in the general automotive and racing communities.
This is a "break-in" coating applied to the skirt of the piston only, designed to show wea
Actually, there had been high-temperature paint before then, but Leonard's and Jeff's visions were instrumental in spawning what is today a continually growing industry on the motorsports landscape. Literally sold from out of the back of his car (when we first met), his Tech Line Coatings are now prominent among companies who either coat parts or make the materials to do so. Also included in the story are some thoughts and experiences from an engine builder well known to the CT audience, Dennis Wells. But first, let's examine some of the basic coatings and their applications. Overall, the message here is that the variety and range of coatings for motorsports use is so vast that you need to conduct your own research to make certain choices are correct for your application. A little time spent in this effort can pay large dividends when the parts are put into service.
Essentially, this continues to be an expanding frontier. However, it's probably safe to identify the more fundamental applications. These include coatings that provide a thermal barrier, those aiding the containment or dissipation of heat and others that address corrosion or chemical invasion. It is interesting that you can also find these various methods to combine for more than one purpose. For example, it's possible for a coating that is a so-called "thermal dispersant" to also combat corrosion.
Perhaps the best approach here would be to categorize coatings into four groups; (1) thermal barriers, (2) thermal dispersants, (3) dry film lubricants and (4) those addressing chemical or corrosion resistance. By first discussing these categories, we can then move to specific parts application.
Smokey Yunick discovered that valve springs raise the operating temperature of engine oil
Thermal Barriers - The transfer of heat (differences in temperature) is a time-based process. Stated another way, it is the conductivity path that resides between two different temperatures that affects the rate of heat transfer in a given period of time. For example, some materials are virtually non-conductive. Such insulators can be used to maintain the heat of combustion both inside an engine's cylinders and along its exhaust path, reducing power loss by the retention of heat (energy) within the system. Ceramics are commonly found in this group.
Thermal Dispersants - These materials aid in the control or rate of heat dissipation. Bringing materials with high rates of thermal conductivity into areas where you'd like to disperse heat has been a traditional method that aids accelerating heat release. So-called "heat sinks" and black paint have been commonly used. However, it's now possible to select specific coating materials that do the job as well or better. It is in this area that combinations of such materials enable a more precise control of how fast and where excessive heat is directed away from critical areas.
These lifters feature a special DLC coating. DLC stands for diamond like carbon which crea
Dry Film Lubricants - These are the friction reducers, sometimes called "solid film lubricants." Far surpassing the benefits of bygone molybdenum disulfide suspended in lubrication oil, dry film lubricants are highly effective in reducing friction, heat, and surface galling. Since the lubricity portions of these materials are what provide the benefits, it's important that a good binder be utilized to keep the lubricants in place. Aside from gains made in friction reduction (particularly friction horsepower), the companion benefit is in heat reduction at the working surfaces.
Chemical or Corrosion Resistant Coatings - Materials in this category serve two fundamental purposes; (1) extended product durability or use life and (2) maintenance of appearance. We'll touch on specific areas where these coatings are of value a bit later.
In the same order they were previously presented, let's examine some specific uses for the coatings categories discussed.
Thermal Barriers - Here, the obvious areas are the combustion space and exhaust gas path. As mentioned earlier, my first and disappointing experience coating piston crowns showed power gains but damaged parts. Fortunately, with today's coatings technology, such problems are passe. So as you might expect, coating piston tops (and bottoms), combustion chambers (in certain applications), the faces of intake and exhaust valves, and complete header systems with these type of heat-retention coatings can be of particular benefit. Keep in mind that power equates with heat in a controlled environment. Therefore, combustion heat lost to cooling systems, combustion surfaces (all of them), and along the exhaust path can combine to reduce net power. Your best bet is to either consult with your choice of parts manufacturer already providing coated parts, or identify a good supplier of coatings materials if you elect to do the job yourself. And don't rule out the latter. Given the current state of some "kits" that are user-friendly to the engine builder, you can also get good results by these methods.
This camshaft has a new pro plasma nitriding process that enhances the performance all aro
Thermal Dispersants - Wherever you find that heat buildup is a concern, these are the materials to consider. Such components as brake parts, oil pans, radiators and intake manifolds all can fall into the need for rapid heat transfer or control. In areas where continual and/or repeated temperature spikes occur and you need to move heat more quickly away from these locations, consider these coatings to be of value.
Dry Film Lubricants - Remember, simply stated, friction horsepower is the arithmetic difference between indicated horsepower and brake horsepower. Therefore, the lower the friction horsepower, the higher the brake horsepower. So, by the use of dry film lubricants in areas that will net a reduction in friction horsepower, you can expect net power gained at the flywheel. Also expect a reduction in both surface and component operating temperatures. Applicable parts include valve springs, engine bearings, camshafts, and piston skirts and pins. Once again, you have the options of either selecting precoated parts or consulting with one of the coatings providers. Should you decide on the first option, it's wise to spend time talking with the manufacturer about the material (and its benefits) on any precoated component.
In this section, it may be helpful to discuss the benefits from coating certain major engine components. We'll include a few reasons and their basis, too. Our intention here is to stimulate some thoughts to the extent you'll begin to identify other parts and how they may benefit from coatings that address specific problems.
Valve Springs - Smokey once contended that valve springs raise the operating temperature of engine oil more than combustion heat. He'd already discovered that with his own version of today's "Spintron" spin fixture. Included in that discussion was his belief, other than valve float, that heat foreshortens spring life more than anything else.
Essentially, there are two sources of heat in a valve spring. One is derived from the friction of a spring moving against other surfaces (inner springs, harmonic dampers, etc.) and the other from the "flexing" or "working" of spring material during normal operation. Studies have shown that a valve spring is never motionless, even when the valve is seated. Residual energy and harmonics traverse an otherwise "static" spring, while the valve is on its seat. Consequently, heat within spring material is continually being generated. Heat is a principle source of damage to springs and, since valve springs are cooled by oil, you can expect other parts of the engine to correspondingly experience increased oil temperature.
This top ring groove coating creates a hard mating surface which virtually eliminates micr
Further, because the distribution of heat in a valve spring tends to not be uniform, coatings (particularly of the dry film variety) can both reduce overall spring temperature and create more uniformity in how the heat is distributed in the spring. The latter of these two benefits goes to the issue of eliminating "hot spots" within spring material, likened in a sense to what you might find from stress risers in other engine components.
In addition, valve springs don't necessarily wear in a uniform fashion. Consequently, coating them with a thermally dispersive material can aid in creating a more uniform distribution of heat within the spring. What you need to avoid are coatings that tend to insulate oil from the spring, thereby preventing the lubricant from absorbing unwanted heat. This can be a particular problem in multiple spring sets where the additional friction surfaces tend to increase temperature at a greater rate and cause the cooling benefits of the oil to be even more critical.
Cylinder Heads - There are multiple areas that can benefit from coating portions of cylinder heads. In particular, coated combustion chambers can increase heat rejection, thereby maintaining more heat in the form of piston-delivered pressure. A more uniform thermal distribution on combustion surfaces has a tendency to suppress detonation, even allowing an increase in mechanical compression ratio. Plus, as you would expect, corresponding changes to ignition spark timing and fuel enrichment can provide additional power.
Increasing heat retention in the combustion space can also lead to less cylinder head distortion from thermal loading, plus reduced coolant temperature. By coating cylinder heads in the valve spring area, some additional heat control is possible. Intake and exhaust ports can also be coated for net gains in power, particularly on the intake side where an air/fuel charge temperature reduction is beneficial in helping reduce tendency toward detonation. Especially at higher engine speeds, coated exhaust ports will aid net flow and reduce heat transfer into the cooling system.
The thermal barrier crown coating is applied to the top of the piston and is designed to r
You may also find it interesting that properly coated combustion chambers can lead to an increased burn rate, thereby requiring somewhat less spark timing. From previous discussions, you will recall that when it's possible to reduce spark timing (from a quicker burn) without an initial loss in power, a net gain in torque can result from a reduction in negative torque (pre-TDC pressure on the ascending piston). In effect, more of the burn occurs near TDC than further afterward. Coating intake manifold surfaces can help retard cylinder head heat into the manifold and, therefore, provide some temperature reduction for inlet air/fuel charges. The benefits of cooler charge mixtures are well known to the Circle Track readership.
Bearings - Conventional wisdom suggests dry film coatings are the best for coating bearings. Properly compounded, these coatings can withstand loadings (pressure) typically in excess of the bearing's pressure limits. According to Tech Line, it's important to make certain the applied film thickness of the coating (using their dry film material) not exceed 0.0003-inch. This dimension usually requires some degree of burnishing to obtain since the as-coated thickness trends more to around 0.001-inch. The latter of these could affect bearing clearance, once the engine sees service and the film thickness is reduced. It's these type of nuances that suggest you should discuss coating needs with your choice of material suppliers, or else application mistakes could negate any benefits from the process, even to the point of parts damage.
Crankshafts - Essentially, there are two areas of most frequent coatings application. The obvious one is bearing surfaces for improved lubrication and additional temperature control of the oil. The other less obvious is coating of non-bearing surfaces with a material that prevents or reduces the tendency of oil to cling to the crank. Particularly at high rpm (intermittent or sustained), oil escaping past the connecting rod and main bearings tends to "knot" or "rope" around the crankshaft, creating a braking effect and reducing net torque at the flywheel. Properly selected and applied coating on all non-bearing crankshaft surfaces will help reduce or prevent such action on the crankshaft.
Once again, whether you plan to purchase precoated parts or do the coating yourself, it's critical to discuss materials and application steps with your chosen supplier. Bearing fit and clearance issues should be on your discussion agenda, at the minimum.
KoolKote is an aerospace quality hard anodize applied to all surfaces of the piston with a
Exhaust Manifolds - Whether cast iron or tubing headers, there are multiple benefits from properly coating these parts. Aside from appearance, corrosion resistance and surface temperature in proximity to the manifolds/headers, there can be improved exhaust flow and engine performance. Coatings companies often have specific recommendations to make, pertaining to power increases, so you may want to consult with your coatings provider for their take on the subject.
Over time, as the number and type of coatings materials have evolved into their current status, so have the ways to apply them. In many instances, specialized equipment and curing techniques are required, as determined by the material and its application process. However, at the same time, materials have become available that can be applied by the engine builder/racer.
Coatings for cylinder walls, headers, camshafts, valve springs, and pistons (crowns and skirts) are currently available and require only a modicum of equipment and skill level. There's even material suitable for coating racecar floor panels to reduce heat radiating from the exhaust system, if headers are in close proximity to this area. Your best bet is to consult with the coatings manufacturer of choice about material type and application methods.
As previously mentioned, and based on his life-long career building and evaluating a wide range of racing engines, we posed a half-dozen or so pertinent questions to Dennis Wells of Wells Racing Engines.
Q: What was the deciding factor in your decision to try coated parts?
Wells: We'd been seeing some abnormally high oil temperature in one of our Silver Crown cars and figured it would be worth trying. Actually, we couldn't keep the oil temperature down below 300 degrees, and even though I'd heard some coatings could increase horsepower, we were mainly interested in reducing heat transfer into the oil. So we decided to coat the piston crowns and skirts. We figured this would keep more heat in the combustion space and allow less to migrate into the oil. Although I'm not certain what this particular effort did for power, we saw significant reductions in oil temperature.
Q: In your experience thus far with coatings, have you applied the materials yourself or enlisted the services of a coatings company?
Wells: Actually, we decided to try it ourselves. As it turned out, we spent more time doing the preparation steps than the actual coating. The coating and baking in an oven were the easy parts. But I can tell you it was worth the effort. We'd been replacing pistons far more frequently than we should have until we tried the coating. I think later this year we may try to use the services of a coatings company who I'm told have newer materials that they apply themselves.
Q: Have you explored coating other areas of engines and what results have you noted?
Wells: In that same Silver Crown motor we coated the oil pan, crankshaft, rods and valves. In fact, at one point, we rebuilt the engine and didn't have time to coat the pistons. The driver immediately reported the oil temperature was about forty degrees higher. So we tore it down, coated the pistons again and the temperature went right back down to where it'd been when we coated them the first time.
We've also experimented with coating valve springs, but because some of the spring material we're now using, and the fact most of our races are short compared to a Cup track and distance, I'm not sure how much the coating would help. But we did see some benefits early before the springs we're now using. I expect in longer races, especially with multiple spring assemblies, you'd see more benefit that what we've observed in our racing conditions.
Q: Based on friction horsepower reductions and heat retention in the combustion space, have you been able to measure any power gains?
Wells: You know, we've never really tried to nail this down. The fact that coating the pistons had such a beneficial effect on our problem with oil temperature, I've not been too concerned about the effects on horsepower. However, I will say that it would appear we've seen gains around 5-10hp, but I want to emphasize that wasn't our primary goal. Had it been, we might have spent more time trying to figure out how to maximize the possibility. I guess I'm basing this on the ASCS engines we've done with and without coated pistons. These are where we've measured the gains.
Applied to the underside of the piston, this coating is intended to reduce the reciprocati
Q: Have you ever experienced any problems using coatings?
Wells: Not at all. In fact, we've even experimented with coating exhaust ports, along with rod and main bearings. My feeling is that if you ever happen to experience any oil starvation problems, the coated bearings will probably help prevent parts damage, especially the crank. And because I've not wanted to trust my ability to coat bearings, primarily because my concern about clearances, I've used companies that do this on a commercial basis.
Q: If you were to suggest the first place in an engine that would yield immediate benefits, where would that be?
Wells: I think the first place would be to coat piston crowns and skirts. Well, maybe not so much the skirts but crowns and combustion chambers, primarily to help retain heat and make more power. I'm sure there's more there that we've not yet looked into, mainly because our initial reason for using the coatings was to solve an oil temperature problem. I'm certain this has added life to the affected parts, too. In fact, I would probably include the valve faces, especially the exhausts.
Based on his 35 years working with and developing a wide range of coating materials and applications, I chose to share some comments recently made by Leonard Warren. While his views are from the perspective of Tech Line, they nevertheless represent a voice of experience, particularly in the field of motorsports, and clearly include his involvement with the circle track community.
"Over time, many have looked at coatings as a Band-Aid rather than a genuine solution to specific problems. Certainly today, this is a mature technology. I say this based on the fact that outside the motorsports industry, coatings are recognized and accepted as a technological solution to often complex problems. Plus, and this may come as a surprise to some people, the OEMs are currently using various coatings in both general automotive and heavy-duty truck applications. The fact that some of these type coatings are also being used by the F1 teams is further evidence of its global acceptance among some of the best funded teams in competition.
"Confusion exists to a degree because of all the new 'coatings' entering the fray. Surface modification systems using high impact impingement, vacuum deposition, ion impingement and vapor deposition, and chemical treatment (these are variations on anodizing) are just a few. In some cases, the equipment can run into the high six- or even seven-figure costs. Each has its advantages. Where the market needs to focus attention now is not on the 'next' cool coating idea but in evaluating each type of system. Examine the application's needs, ability to handle all the environmental issues found in racing, the overall cost-to-benefit ratio, and potential downsides."
Essentially, there are "coatings" and there are coatings. By purchasing precoated parts, you make the assumption manufacturers have done their homework in selecting the best coating technology for the application. And there's nothing wrong with that. There are clearly some excellent products available. However, whether you elect to take this path or decide to apply coatings yourself, becoming familiar with the basic categories of coatings applicable to a motorsports environment will help eliminate problems derived from either a lack of information or just plain oversight. Talk to the sources and make your selection decisions accordingly.
Lubricating oil can only perform within its inherent limitations Unwanted and/or improperly-distributed heat in an engine is a natural phenomenon and partially a function of power level. Friction horsepower losses are a fact of life. In short, the high mechanical loads and stresses derived in a racing engine are that, in addition to the notion rust and corrosion are ever present. How you deal with these issues should very likely include the benefits of applicable coatings materials. Band-Aids, they're not. Potential solutions to problems, they can become.