To better understand the need for race oils, one should understand the components that comprise oils. There are five types of base stocks, which is basically oil with no form of additive. Group I is only lightly refined, and thus rarely used in automotive applications. Group II is the modern conventional (aka mineral) oil. Groups III, IV, and V are all considered “synthetic,” but are not created equally. Group III is a very highly refined petroleum product that has been the base stock almost exclusively used by street oils since the late 90’s. Groups IV and V are synthesized oils that comprise the bulk of base stocks in race oils. While Group III oils are great choices for the street, they are less robust to heat seen in track cars.
Each type of base stock provides certain attributes, and many good race oils use multiple types. Group IV, most commonly known as PAO (Poly Alpha Olefin), is the primary component in most race oils due to its superior temperature performance and high viscosity index. In some race oils, it is the only base stock used. Unfortunately, it is not polar, meaning it doesn’t stick to metal very well, which results in a poor oil film. It also causes seals to shrink. Group V’s, or esters, have very good, though slightly inferior to PAO temperature performance. However, esters are polar and thus stick very well to metal and give a superior oil film, though the polar nature also interacts with some additives. Esters also cause seals to swell, and are also several times more expensive than PAO. The tendency to interfere with some additives makes the amount of ester base stock in a blend a very important factor. The percent in a blend ranges from none to a high of about 20%. The combination of PAO and ester, in the right proportions, makes for the foundation of a very good oil. Finally, Group III base stocks are still used, typically in small amounts, to “fill out” the remainder of the oil without disrupting the ester/additive and ester/PAO balances, while inherently providing good lubricity.
In addition to base stocks, additives (primarily ZDDP) also factor in oil selection. ZDDP is a thick, sticky, honey-like substance that protects by depositing a layer on, which is subsequently wiped away from, a surface – a cam lobe on a flat tappet is the easiest visual, but the benefits are realized throughout the engine. As mentioned, ZDDP’s use was reduced drastically in the mid 2000’s due to EPA regulations. While modern street cars need only some ZDDP, the extreme environment in which a race car operates drives the need for higher levels.
This is primarily due to the elevated temperature which thins the oil to a degree where its ability to protect the engine without additives like ZDDP is greatly reduced.
While public cognizance of the benefit of ZDDP in highly stressed applications is good, an unfortunate downside is that some oils containing a detrimentally high concentration of it have been made available. Current street oils are limited to approximately 600 parts per million (ppm). Decades ago, the range of ZDDP in oils was around 2000ppm. An optimal amount of ZDDP is generally considered to be 1000-1300ppm. Lower concentrations do not allow a proper film to deposit, and higher concentrations provide no additional benefit, while increasing parasitic drag throughout the engine. The range of ZDDP in most race oils is approximately 1000-1600ppm, but concentrations of higher than 2200ppm are made.
Viscosity index (VI) is another quality of oils gaining recognition in the market. VI is the relationship between cold and hot viscosities. The higher the VI, the less the oil thickens as it cools, making a higher VI a superior quality, all other things equal. A 5w40 will have a higher VI than will a 10w40. Unfortunately, many erroneously assume that the viscosity will extrapolate beyond the 100OC based on VI. Ultimately, the method used to attain a high VI is perhaps more important than the actual value. VI is the result of both the VI of the base stocks, and the addition of VI improvers. VI improvers are polymers that react at different temperatures to increase the VI of an oil blend. They can lead to much a much higher VI than even the best base stocks can provide. The drawback is that VI improvers will shear down, whereas base stocks will not, meaning that an oil using higher quality base stocks will maintain its viscosity longer than a higher VI oil that uses large amounts of VI improvers to obtain that high VI. Many ultra high VI race oils must be changed every few hundred miles due to the shearing of VI improvers.
High temperature, high shear (HTHS) viscosity is perhaps the most important viscosity to consider, yet it is relatively unknown by the public. It is measured at 150OC under a shearing condition, which most closely replicates the condition in an engine’s cranktrain (note that oil can increase in temperature by as much as 50OC as it is worked through the cranktrain). As referenced earlier, extrapolation can lead to erroneous assumptions. For example, a popular 0w50 race oil has both higher VI and hot viscosity than a different brand’s 5w40. However, the HTHS of the 0W50 is only 3.8cP, compared to 4.4cP for the 5W40, which means that in the cranktrain, the 5W40 is a thicker oil than the 0W50!
The race oils on the market appear to follow one of two philosophies with the use of detergents and dispersants (often grouped together, and referred to more simply as detergents). Detergents are cleaning agents, and dispersants keep wear particles suspended in the oil to be captured by the filter. The greater the amount of detergents, the longer an oil will prevent sludge formation. One philosophy is to use very light detergent packs, for a two primary reasons. First, many racers will change their oil very frequently regardless, so the benefit of a more robust detergent pack is not realized. Second, detergents increase the oil’s coefficient of friction, so minimizing them will reduce parasitic losses without other additives that may alleviate that phenomenon.
The other philosophy is a very robust detergent pack. This provides two benefits to users. First, fewer oil changes are needed. One example of this was one shown in one of the Racer’s Edge 996’s, driven by Karl Poeltl in both PCA and World Challenge races that ran a season comprised of 9 races over 5 weekends and 1700 race miles, on a single fill of Millers Oils CFS race oil. After the season, the oil was still robust and within specification. This contrasts with the low detergent oils which typically must be changed in 500 or fewer miles. The second benefit is that it alleviates the tendency of sludge to accumulate long term, even with frequent changes. Cylinder bores, especially the more porous ones such as Nikasil, are inherently prone to becoming clogged with oil deposits from low detergent oils. With frequent rebuild intervals, this may not be a factor, but few club racers operate at a level where rebuilds occur throughout the season.
As mentioned, detergents do increase the coefficient of friction, meaning that a low detergent oil will make more power than a high detergent oil, all other things equal. However, the friction increasing tendencies of detergents are being offset by both the incorporation of ester base stocks and advances in additive technology, such as the nanotechnology used in Millers Oils’ Nanodrive race oils. Some other companies have shown an ability to offset that increase in friction through the use of ester base stocks and other additives.
In conclusion, there are many reasons racers should consider oil selection with a critical eye. And while race oils are expensive, a good oil can lower one’s overall operating cost through better protection and/or prolonged oil life. Be cautious about marketing, as what may generate sales may not be what best protects. Finally, one thing all racers should consider is the use of used oil analyses by a reputable lab. Doing so can not only advise one when his oil needs to be changed due to either viscosity loss from VI improvers shearing down or fuel dilution, or depletion of detergents, but can also tell the user about the overall health of their engine. You might just catch a #2 rod bearing or an IMS bearing on its way out before incurring a catastrophic failure!
From: Bill Comat
Millers Oils Eastern Canadian Distributor