Engine oil selection for a road car can be difficult enough at times when you have to consider manufacturer specifications, application & environmental factors etc. The process can become even more difficult when selecting an engine oil for a track car when you also have to take into account variations in operating temperature, variations in fuel type, increased load and the potential for premature wear of those expensive engine components!
Depending on the type of track car, sometimes an engine oil can be selected by taking into account the original engine manufacturer’s specifications and then building on those to suit the application, such as an Improved Production Car for example. On the other hand if the engine is a purpose built race engine then the engine oil selection may need to be made with input from the engine builder including information like component machining tolerances & clearances. In some cases the engine builder may only warrant an engine if their recommended engine oil is used for that particular engine type or application, such as a V8 Racing Ute.
High operating temperature is one of the biggest killers of an engine oil and in a track car these conditions are almost guaranteed. Viscosity can reduce significantly and additives such as the anti-wear, detergent & dispersant chemistries can be adversely affected if the oil temperature is too high. This can sometimes be combatted by external means (oil cooler) but it is still important to have the most stable engine oil for high operating temperatures and a full synthetic is the best in these conditions. Synthetic base oils are made up of extremely pure molecules that are more resistant than mineral base oils to things like oxidation, particularly when they’re hot. Other than the base oil type, when selecting an engine oil viscosity for a track car an allowance for increased temperature needs to be made in order to ensure adequate film strength and oil pressure.
Something to keep in mind is that the anti-wear, detergent & dispersant chemistries in the engine oil have an optimum temperature range in which they are most effective, usually between about 80°c and 100°c. Outside of this range they are less effective, which is one of the reasons that engine oil can form sludge in a road car that’s only used for stop-start driving as the oil never gets up to temperature. Due to this it’s always advisable to warm your track car engine to operating temperature so that the engine oil can clean and reduce surface wear effectively.
Along with variations in temperature, fuel dilution of the engine oil can also dramatically decrease viscosity if it isn’t managed correctly through regular oil changes and oil/air separation devices. There are some instances, such as in drag racing, where mineral engine oils are traditionally preferred usually because of their ability to absorb contaminants. This can include fuel from blow by due to extremely high cylinder compression & forced induction although the synthetic engine oils that are available these days are better at this now than when they were first introduced years ago.
Fuel compatibility becomes more of an issue with a track car due to the variety of fuels used and one of the biggest concerns is hygroscopic alcohol based fuels like ethanol or methanol and the water they introduce. If running an alcohol based fuel, try to choose an engine oil that meets API SN specifications where possible as there are additives included in these engine oils that are specifically designed for alcohol compatibility. There is also an emulsion retention test that API SN oils have to pass in order to verify their ability to manage the water introduced by the fuel.
With increased horsepower comes increased load and the engine oil needs to accommodate this to offer adequate protection. In a hydrodynamic lubrication situation an engine oils film strength, along with velocity, is what allows it to support a load between two engine components such as piston ring and cylinder liner, camshaft lobe and follower, bearing and crankshaft etc. Generally the higher the viscosity the higher the film strength however heavy viscosity oils can rob the engine of power due to viscous drag and the extra energy required to pump heavy oil around the engine. It can be a compromise between power and protection although for some engines power is in abundance and the little extra required to pump a heavy engine oil around can be worth the extra protection, such as Top Alcohol Funny Cars that usually run an SAE 70 viscosity grade.
Sometimes in cases of extreme loads even the heaviest viscosity grade engine oils cannot maintain film strength and support the load by keeping the surfaces apart, the oil film can separate and boundary lubrication can occur which can result in some metal on metal contact. In these instances engine protection is then reliant on the friction reducing & anti-wear additives like Moly DTC & ZDDP to reduce component surface wear. This is particularly important in ‘flat tappet’ camshaft arrangements especially while the nose of the cam lobe rides over the tappet.
Under these extreme loads and at high temperatures the ZDDP (Zinc dialkyldithiophosphate) reacts and forms a sacrificial layer on both of the component surfaces acting as a final barrier of protection. The Moly DTC (Molybdenum dithiocarbamate) also reacts and forms sheets of molybdenum that build up between the component surfaces allowing them to slide past each other with a dramatically reduced friction coefficient. The combination of these additives provides the best anti-wear and friction properties and it is crucial to have adequate levels of them to reduce components surface wear.
It all comes down to the application you are using your car for, take the time to do your research on the different viscosities available on the market and make and educated decision on which oil to run in your track car.
for more information on oils and lubricants stay tuned to the Nulon blog.