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Three Reasons to Wear a Coat
Every engine builder worth his salt knows that coatings can be used to great effect when trying to persuade the forces of physics to co-operate with your plan of making a big piece of metal go really fast by using explosions and lots of moving parts.
What’s not usually as well known is the incredible versatility that coatings have in dealing with a huge range of problems.
The number of uses for various coatings in performance applications is mind-boggling and nearly limitless, but in order to keep the possibilities cost effective and manageable it’s useful to think about it in terms of the three most common problems that coatings are used to address.
The big three we’re speaking of here are:
These three factors play a huge role in determining the power potential, efficiency and durability of an engine. So when evaluating how you might solve a problem or create a benefit where one of these elements is involved, a coating may be worth consideration. There are also cosmetic benefits, of course, because a lot of coatings can be made to look very cool, but for purposes of this article we’ll stick to performance uses.
Friction reducing coatings are commonly used on engine bearings, piston skirts and other similar applications to reduce wear. Durability applications probably offer the most bang for your buck with these sort of coatings, often extending the lifespan of pistons or crankshafts well beyond what they would normally reach.
However, there are also a multitude of less common applications for these sorts of coatings that can be used to enhance performance. Turbocharger units are sometimes coated internally in order to increase power output by reducing resistance to the flow of air, this is a particularly interesting application since people rarely consider the effect friction can have on airflow itself.
Another type of coating, applied to the piston wrist pins, allows for decreased friction in an area where an oil film is not present during normal engine operation.
Areas that are not oiled, but whose operations are affected by friction are prime targets for the flexibility of a coating. Conversely, some anti-friction coatings make use of their properties in areas where retention of oil is actually undesirable, for example, a coating can be applied to crankshafts that sheds oil in order to reduce windage. That is not to say that low friction coatings in areas that are oiled regularly should be limited to those areas that need to shed oil. It has been shown that certain low friction coatings applied to key oil lubricated areas can actually lower oil temperature by a significant margin, allowing for the use of thinner oil.
The bulk of useful engine coatings that are not friction reducers are thermal control coatings. These coating generally come in two flavors, the first being thermal barriers. Reflective barriers often increase combustion efficiency when applied to valves, combustion chambers and piston tops. The same type of coating also sees frequent use externally on intake manifolds, helping to keep the incoming air cool, and has varied uses throughout the exhaust system. It’s not hard to imagine a multitude of other applications where keeping heat out could solve a lot of problems.
The other common class of temperature control coating is the thermal dispersant, designed to help coated areas shed heat more efficiently. Thermal dispersants are especially useful when applied to valve covers or on the oil pan itself, helping to draw unwanted heat from the oil. Outside of the oil system, dispersants have the flexibility to perform a range of functions, from increasing the efficiency of the intake manifold to dramatically extending the lifespan of the valve springs.
Many coating blends designed for these purposes also have good frictional properties. The previously mentioned frictional coating used on turbochargers, for example, is also designed to trap heat inside the unit, increasing thermal expansion and, therefore, power output. In some cases, alcohol engines have made use of a special "Teflon" blend coating on the injector hat to prevent the butterflies from icing over, making use of a frictional blend to address a thermal issue.
Alcohol and methanol engines face special challenges when it comes to corrosion. Coatings using a blend of fluorinated polymers are often used to address the harsh effects of these fuels on piston skirts, bearings and on valve springs. As with the thermal coatings above, many of these are formulated to provide frictional benefits as well, making them doubly useful.
Coated Oil Pump
Other types of anti-corrosive coatings see frequent use in the marine performance field, where the destructive effects of salt water on both iron and aluminum heads and blocks would be otherwise unmanageable.
When considering the use of coatings for any given application it is, perhaps, most important to know that various coating agents can be blended to produce any number of combined effects. An expert can combine thermal, frictional and anti-corrosive properties to produce a formula tailor-made to a wide range of potential specifications. Given the number of engine components that are adversely affected by more than one of these three elements, blended coatings have some of the most intriguing possibilities for creative use.
Professional racing teams make use of a variety of unusual coatings in order to get an edge on the competition in an extremely competitive environment, but it is becoming increasingly common for street rodders and weekend racers to nab a few choice coatings that have the most significant effect on horsepower, or to save cash by extending the lifespan of expensive components that see a lot of wear.
If you’re looking to get some extra value out of your performance engine, coatings are definitely something worth considering.
Source: Dart Machinery