Racing Oil vs. Street Oil: Know the Differences
The difference between racing oil and street oil is largely characterized by the base oil chemistry and various additive packages specified by engine manufacturers. Additive packages contribute multiple levels of lubrication efficiency and protection — including anti-wear, friction reduction, rust and corrosion resistance and detergent and dispersant qualities — that help keep engine internals clean and functioning properly.
Effects of racing on oil
Here’s what racing oil looks like after 500 miles in a NASCAR engine. On the right is fresh 20W-50 synthetic racing oil, and on the left is oil pulled from Mark Martin’s Ford following his victory at Fontana in 1998. The discoloration is the result of oxidation, which is caused by heat, soot and other combustion carbon byproducts that blow by the rings. Those engines produced about 700 horsepower. Today’s Cup engines run 5W-20 synthetic oil and make close to 900 horsepower.
“Just like cams are ground differently for street driving versus superspeedway racing, high-performance street oils are formulated differently than racing oils — due to the subtle differences in each application,” explains Lake Speed, Jr., a certified lubrication specialist at Driven Racing Oil. “The little details make a big difference.”
“Racing oil is more heavily fortified with additive systems to give the performance to protect the engine,” sums up Mark Negast, technical director at Lucas Oil Products. “Still the same additive systems, just higher concentrations.”
“Racing oils are formulated without regard to emissions equipment life,” adds Chris Barker, technical services manager at Royal Purple.
Today’s late-model cars are well served by contemporary, over-the-counter motor oils. These formulas evolved with complementary qualities engineered to accommodate a broad range of operating conditions, including catalytic converter preservation and long-term emissions compliance. But many contemporary motor oils have reduced anti-wear qualities as late-model engines enjoy fewer critical high-friction challenges. That leaves early performance engines or modified racing engines equipped with flat-tappet cams and high valve-spring pressures at risk with current motor oils.
“Anti-wear additives come in many different formulations with each major additive supplier offering multiple versions of differing efficacy and molecular structure,” says Barker.
Different additive packages
Oil suppliers incorporate additive packages they deem necessary to meet the requirements of specific applications. To maintain consistency throughout the industry, the American Petroleum Institute (API) — working in concert with major automakers through the trade group, International Lubricants Standardization and Approval Committee (ILSAC) — recommend voluntary minimum performance standards and chemistry restrictions. All API and ILSAC licensed oils are suitable for any production passenger car or light truck with a stock engine. Those formulas, however, may not provide enough protection for modified performance engines, particularly during engine startup and break-in.
Zinc, along with phosphorus, sulfur and sometimes other elements, comprise these anti-wear additives. The most common are a family of compounds generally referred to as ZDDP, or ZDP, which stands for Zinc Dialkyl Dithiophosphates. In engine slang, ZDDP may be simply but incorrectly referred to as “zinc.”
By itself, the element zinc provides absolutely no benefit in engine oil. The chemical compounds containing the additional elements actually provide the sacrificial phosphate layer that, under high pressure and temperature, protects highly loaded sliding surfaces against wear damage.
“There are many different ZDDP chemistries with varying levels of quality and performance,” adds Barker.
Understanding anti-wear additives
Matching viscosity and clearances is critical.
— Lake Speed, Jr.
All engine oils still contain anti-wear additives, though in lesser amounts than previous generations, due to concerns for emissions equipment life. The chemistry restrictions set by API originally targeted only phosphorus — which can be harmful to catalytic converters — and currently stand at 800ppm (parts per million). Phosphorus is typically only found in anti-wear additives, so a restriction on total phosphorus puts a restriction on the total additive. Along with phosphorus, the chemistry restrictions also address “ash” content, which is determined by weighing the residual left after a measured amount of oil is boiled and burned away. The various additives contained in engine oil, including anti-wear additives, contribute to total ash content.
The decrease in anti-wear additives coincided with steady improvements to additive chemistry and oil formulation across the board. Though modern engine platforms have incorporated lower-friction components to reduce the need for anti-wear additives, new production engines also have a much greater power-to-displacement ratio and a life expectancy in excess of 200,000 miles. Engines from the 1970s and early 1980s during the “high-zinc era” were lucky to achieve 100,000 miles before a rebuild was required. With every new API oil specification, the requirements for wear protection, corrosion protection, and cleanliness increased, in spite of an overall reduction in anti-wear additive.
ZDDP can be described as a polar molecule whose protective qualities are activated by heat and load. Different families of ZDDP are classified by their burn or activation rate and percentage of ZDDP in relation to detergents, rust inhibitors and other components.
“ZDDP additives with faster activation rates are more suitable for racing and high performance street engines with challenging friction characteristics, such as flat tappets or new engines undergoing break-in,” says Speed.
Performance oil manufacturers address anti-wear concerns each in their own way. Driven’s racing and street performance oils are characterized by increased levels of ZDDP and dramatic reductions in detergent levels to achieve high anti-wear characteristics. In part, this strategy is based on projected frequency of filter changes and drain intervals typical of street performance engines with infrequent use.
ZDDP and detergents
“For higher rpm and horsepower, you might see lower concentrations of calcium,” echoes Negast. “Typically what happens is the calcium competes for area surface with the zinc and phosphorus. In NASCAR and IndyCar, you’ll see a reduction in calcium detergents because they’re not necessary. In NHRA, you don’t need detergent at all, just wear protection.”
However, Royal Purple points to SAE papers showing that certain families of ZDDPs and detergents actually perform better when combined.
“An engine oil with little to no detergency and with excessive anti-wear additives will result in excessive engine deposits,” says Barker.
While the different companies offer a wide range of high quality lubricants with chemistries developed according to their individual philosophies, the following criteria should be considered when choosing the best oil for specific applications: engine speed, engine load, operating temperature, engine content (flat tappet, valve-spring pressure, etc.), operating clearances and operating environment.
High piston speeds in race engines also affect the engine builder’s choice of oil. Cylinder wall and piston skirt lubrication are normally covered by splash oil coming off the rod bearings and the camshaft. But as piston speed exceeds 5,000 feet per minute, the hydrodynamic oil film between the piston skirt and the cylinder wall begins to lose effectiveness, which will cause pistons to scuff. The minimal fog of lubricant in the crankcase has no time to attach itself to the cylinder wall. The problem is exacerbated in dry-sump applications that remove oil from the pan very quickly. Also, some engine-block designs isolate the cam tunnel to eliminate cam and lifter oil from dripping on the crankshaft. All these racing modifications reduce the amount of oil being splashed on the cylinder walls. Racing oils with properly specified additives and correctly matched viscosity for the application and operating clearances involved can help provide protection where pin oilers are not available to help splash lube the walls.
‘Lubricity’ in race and street oils
One lingering myth about racing oil is that it has more “lubricity” than street oil. Simply not true. The additive packages required for production engines do not affect the oil’s lubricity.
“All engine oils for automotive use want as much lubricity as possible,” explains Barker. “Oil companies or automakers won’t specify fewer lubricity agents unless there’s a downside. The differences between race and street oil all comes down to the chemistry restrictions associated with the API license.”
Cooling is another vital and often unrecognized function performed by engine oil. It encourages component longevity, so engine builders spray oil on the valve springs, camshafts and the bottom of the piston crowns to keep them cool. These components operate in a severe temperature environment and maximum oil performance is required to support them. Conventional mineral oils are comfortable up to about 260°F while the superior thermal qualities and shear resistance of synthetic oils still provides protection even above 300°F without viscosity breakdown.
When choosing engine oil, picking the appropriate viscosity grade is extremely important. Automotive engines are typically tolerant of viscosity, but go too far to the light or heavy ends of the viscosity grade scale and the engine will suffer suboptimal performance and protection, if not actual damage.
Some smaller import and domestic engines do not tolerate viscosity changes well. For example tiny valve train components with very small clearances may experience a stacking (hydraulic) effect when heavier oil is used regularly. Over time this can result in valve train damage and even broken valves due to fatigue. Follow the engine manufacturers recommendations with regard to the weight of the oil you run.
There is a difference between viscosity (a measured value) and viscosity grade (which spans a range of measured viscosity values). The measured viscosity of a particular oil changes constantly with temperature. The viscosity grade of an oil (e.g. 10W-30) does not change unless the oil is actually damaged.
There are three parts to the SAE viscosity grade. The last number (20, 30, 40, etc.) defines the “major” grade. It is determined by the oil’s measured viscosity at 212°F (100°C) and is the most important part of the viscosity grade. It should be considered the operating, or effective viscosity grade of the oil. The “W” stands for “winter”, and not “weight” as is commonly believed; and the first number combined with the W is the “winter grade”. The winter grade of a multi-viscosity oil is determined by two parameters: the Cold Cranking Viscosity; and the Pumping Viscosity. These viscosities are defined as maximum viscosity values at various sub-zero temperatures. All of this is defined by SAE J300 (see chart).
The selection criteria shown in the chart (below, courtesy of Royal Purple) influence the optimal choice of viscosity grade. For example, two identically built engines would likely have different optimal viscosity grades if used in different racing disciplines.
“Operating temperature really impacts oil formulation and viscosity selection,” warns Speed. “High-temperature applications like Sprint Cup utilize different chemistries than low-temperature applications like Pro Stock.”
Matching viscosity to engine clearances
Viscosity must be properly matched to the engine’s clearances and operating conditions to optimize performance. If an engine is not built to take advantage of light viscosity engine oils, the oil may not be able to adequately “fill” the oil clearances and fail to adequately support engine loads. On the other hand, heavy viscosity grade engine oil does not automatically equal better protection.
“Oil film strength and high-temperature, high-shear viscosity are the essentials to providing optimum bearing protection,” says Negast.
There’s an old engine builder’s adage about clearances says that “loose is safe.” That’s generally true, but some builders flirt with disaster by running wider clearances and using thinner oil that can’t support them. The pressure distribution of any bearing is typically greatest at the center and tapers off toward the edges as the bearing discharges oil to the side clearance. Hence, wider bearing clearances require a higher viscosity oil to maintain the hydrodynamic oil wedge while tighter clearances will support thinner oil at the right pressure.
“Whether you realize it or not, you build your engine around the oil so matching viscosity and clearances is critical,” says Speed.
Some street performance oils balance higher ZDDP levels with less detergent, but you can still race and change every 3,000 miles. Others do not sacrifice detergency and oil cleanliness, and still maintain exceptional wear protection for extended drain intervals. The oil manufacturer’s tech line should be called to determine the useful life of their products.
Racers, however, must be aware of oil condition at all times. Oil is easily diluted when using nitrous or alcohol.
“Some racers will try to burn off the alcohol and reuse the oil,” says Negast.
Specially designated break-in oil is a must for all fresh engine builds/rebuilds to ensure adequate wear protection for the valve train, while allowing the new piston rings to seat to the engines cylinder walls. It provides a balanced package, plus corrosion resistance and rust and inhibitors. Engine builders can then switch to the preferred racing or street-performance oil.
“Once a new engine’s parts have achieved compatibility with a good high quality break-in oil,” confirms Speed, “most street engines can still operate safely on modern over-the-counter street oils.”