All about oil for street and autocross use
Industry specialists set the record straight on motor oil for classic cars
Photography Credit: Dave Green
Picture the spinning, rocking, whirling parts inside an engine. Now spin those same pieces to hundreds of thousands of revolutions per hour in a competition environment. And let’s do it for a few hours at a time with little to no mechanical empathy. No rest, no recovery, no thank-you from the podium.
What keeps those parts from welding together into a giant pile of slag? A thin, thin film of hot oil–an oil that, after the race, is usually unceremoniously dumped from the engine and replaced.
We ask a lot of our oil, especially on track. But do we know all of the answers? That’s where our expert panel comes in.
A properly formulated racing oil is designed specifically to deliver the benefits racing engines need, such as improved extreme-heat resistance, maximum friction reduction for optimum power, and increased film strength to protect bearings in powerful, high-torque engines.
Passenger car motor oils, on the other hand, are designed with fuel economy and longer oil life in mind–benefits racing vehicles don’t need since the oil is changed frequently. Use an oil designed specifically for racing in competition vehicles.
–Len Groom, technical product manager, Amsoil
Think of shoes. The type of shoes that Usain Bolt wears is very different than the type of shoes a Paris runway model wears. Both are shoes, but they are each designed and manufactured for specific purposes.
–Lake Speed Jr., certified lubrication specialist, Driven Racing Oil
The answer depends on so many factors, including what you mean by “race.” Is it a quarter-mile drag competition, a dirt-track rally, a 500-mile oval run, or a few laps around cones in a parking lot?
In general, any type of racing stresses oil more than daily commuting does. That’s especially true where exotic fuels are employed and cars are significantly overfueled (which leads to fuel dilution in the oil). This is the reason nitro-fueled NHRA dragsters get an oil change every time the engine is turned on.
Most other professional race teams change the oil after each race–except where prohibited by rules. Amateur racers typically change oil based on prior experience at the specific circuit.
–Valvoline Technology Team and compiled by Josh Frederick, OEM technical manager
As an oil technician, I would be inclined to maintain a more frequent, carefully selected drain interval in any racing application. I often ask, “What is more important to an end user: extending the oil drain just because you can, or maintaining a safe drain interval?” In racing applications, the more frequent, the better. After all, the end user is dealing with the lifeblood of the engine.
–Kenneth M. Tyger, director of Technical Services, Penn Grade/PennGrade1 Lubricants
This should be determined by used oil analysis. Anything else is just a guess, and the high value of a race engine warrants some actual science.
–Lake Speed Jr., certified lubrication specialist, Driven Racing Oil
Most pro teams take samples after every race and have them analyzed to determine if there’s any wear or unusual byproducts in the oil. This helps them decide if they are using the proper oil, if they need to replace the oil more often, and possibly warn them of any pending problems, like a leaking head gasket.
–Stefan Braun, application specialist, Liqui Moly
This is application-specific. Most operating oil temperatures run between 180 and 220 degrees Fahrenheit, but various racing engines can run as high as 300 degrees. When an application runs well above 300 degrees on an intermittent basis, most high-quality conventional, mineral-based engine oils can typically handle it. When oil temperatures reach well into the 350-degree range on a continuous basis, the end user must drain their conventional oil more frequently or consider a full synthetic.
–Kenneth M. Tyger, director of Technical Services, Penn Grade/PennGrade1 Lubricants
Once again, this depends on the design of the engine. Turbocharged engines usually run much hotter–sometimes 250 to 300 degrees Fahrenheit. Generally, you want to try to keep the oil in the range of 220 to 260 degrees Fahrenheit. Temperatures above this may raise evaporation loss and shear issues.
–Michael Trueba, MPT Industries
The first place to look when attempting to determine the proper engine oil viscosity for your racing application is the engine manufacturer’s specifications. Although high-temperature operation may require a slightly higher-viscosity engine oil, you don’t want to jump up too high. If you do, you may hamper the ability of the oil to properly flow, decreasing its ability to lubricate properly.
If, for example, the manufacturer specifies the use of a 10W-40 engine oil, you may want to move up to a 20W-50. However, if the manufacturer specifies the use of a 5W-30, you most likely shouldn’t increase the viscosity beyond 10W-40.
If you notice that the motor oil temperature is increasing beyond the acceptable range, move up to a higher viscosity.
Keep in mind that engine clearances and tolerances, as well as the type of racing, are also determining factors in the proper selection of oil viscosity. If the clearances and tolerances are tight, the engine will require a lower-viscosity oil. Also, sprint races generally require a lower viscosity than endurance races.
–Michael Trueba, MPT Industries
The oil viscosity (in Centistoke value) should be determined by bearing clearance, and the SAE grade should be chosen to deliver that Centistoke value at normal operating temperature. We have a chart [in our catalog] that shows the correct SAE viscosity grade for the bearing clearances and oil temperature.
–Lake Speed Jr., certified lubrication specialist, Driven Racing Oil
Oil temperature doesn’t always equate to the weight of the oil. Oil temp is important, yes, but not the only thing to look at when making your choice. Don’t forget oil coolers, etc.
Determining the ideal viscosity involves a variation of things. Here’s an illustration of how hard it is: In drag racing–specifically the Pro Stock class, where they use 500-cubic-inch engines that produce 1500-plus horsepower–a 0W-5 or thinner oil is often used. NASCAR uses similar viscosities during qualifying. The important thing to remember here is that the oil temperature in these engines usually never goes very high–only 100 to 140 degrees Fahrenheit.
Compare this to Turner Motorsport in IMSA’s GTD class. The team uses a Liqui Moly Leichtlauf High Tech 5W-40 oil in its BMW M6 engine. The oil temperature is usually 220 to 250 degrees under normal circumstances, with occasional temps upward of 300 Fahrenheit.
What does this tell us? There’s very little difference in actual kinematic viscosity between the above examples. Turner uses an oil that has an approximate dynamic viscosity of 10.0 to 12.0 Centistoke at its normal operating temp, whereas Pro Stock engines use an oil that’s very close to that same viscosity at its normal operating temp–which is about 100 to 130 degrees cooler.
Most privateer racers use either a 20W-50 or even a 10W-60 oil. The quality of the oil will determine how well it stands up to the heat and protects your engine. A thicker oil may be okay as long as the engine is warmed up to reach the proper oil temp and kinematic viscosity.
A good indicator of a quality oil is its viscosity index: A higher number is better.
–Stefan Braun, Application Specialist, Liqui Moly
Based on the viscosity recommended by the engine manufacturer, select a racing oil that will be up to the task. For example, endurance racing requires an oil that can handle high heat without thinning
or evaporating too much. Review the oil’s Noack Volatility and high temperature, high shear ASTM test results and compare them with others.
–Michael Trueba, MPT Industries
Use the OEM-recommended viscosity.
–Len Groom, technical product manager, Amsoil
Again, give the car what it needs. Make sure the oil you use is spec’ed appropriately. If it’s a German car, make sure you use an oil that has the official approval.
–Ole Wagenbach, Rowe USA
It’s best to consult the tech department of the oil company. There are too many questions to ask and answer here.
–Lake Speed Jr., certified lubrication specialist, Driven Racing Oil
Only when you have no other choice or if your race engine builder insists. A straight-viscosity oil (20W, 30W, 40W, etc.) may be too thick on cold startup.
For example, if your garage is 32 degrees Fahrenheit and your car is running a 40W oil, that oil would take 60 seconds or more to flow to the farthest area from the oil pump. That means until then, part of the engine would be running without lubrication.
Of course, you may be able to get by with an oil heater that preheats the oil, but usually only race cars have these.
–Stefan Braun, application specialist, Liqui Moly
I like and take both of your magazines and have been waiting for these articles to answer several questions I have for 3 different vehicles: a stock 1967 230SL Mercedes, a highly modified 1970 Camaro - carburetted 383 that produces about 450HP and a 1987 300ZX race/track car.
I am disappointed with this series of articles. There really appear to be 2 or 3 standard answers; perhaps dictated by the respective corporate lawyers. Answer 1: "follow the manufacturers recommendation". Answer 2: "buy our specially formulated oil". or "follow your engine builder's recommendation". None of those 3 answers really helps me. Or would cost me a lot more than solutions I think exist.
Let's take each car and it's respective problem. I would like to "improve" the oil in the Mercedes by using a newer synthetic but would also like the protection of ZDDP since there's no catalyst. My question would be: what modern full synthetic should I use and how much ZDDP should I add per quart?
The Camaro is much the same but a bit more of a mystery. I have NO idea who built the engine and suspect that if I could find him/her their answer would be suspect and based only on their respective experience. So, again the same question: what modern full synthetic should I use and how much ZDDP should I add? I'm currently using a 10w-40 with a pint of ZDDP for the full change of 7 qts.
Last is the race car that competes in ChampCar endurance races. The engine is required to be stock and the recent "Rockauto" rebuild was done by me, my son, and a local machine shop that honed the cylinders. Clearances and rebuild components are stock or OEM replacements except for a reground cam. Pan has some windage control but other than tuning it's stock and produced 175RWHP on the dyno/tuning run. We would like to run an over-the-counter full synthetic and perhaps add some ZDDP (we are curently running a rbeak-in oil).
All of these cars are DIY cars and we operate on tight budgets for each. So, please don't tell me I need to buy $10-$15 per quart oil when I can get good modern full synthetic for less than 1/2 that price. I suspect that many of your readers have similar challenges. Perhaps your experts need to be off the record.
In reply to russelljones48 :
Agree 100%
Even when we were running the modified big block Chevy we didn't use any "race oil" Just off the shelf Havoline.
Just a little info on the dyno we found that on our 500 ci engine we made close to 35 extra hp with one quart less oil in the engine and also another 15 for 0 W 20 synthetic oil. I would not recommend you race this way depending on what type of racing you do. Drag racing we can get away with it, but I would just look at what you see on the dyno as you run it up for your tune up. One of the things we look for is oil temp and viscosity as it warms up, then as we run it through its paces with about 10 pulls. the test stand has gauges to check remotely from the control room and a video on the board to make sure we don't miss anything, when celebrating when we make more then we anticipated.
In reply to russelljones48 :
Sounds like you're off to a good start. Most of the information you're looking for is actually in the article but then you have to search for a few more things like go to driven oil and find their bearing clearance chart which is easier to find via Google. If we take your track car for example because it takes the most extreme use then probably a 5W40 mobil one full synthetic would be good. I has about a 3.5 HTHS and about a 13.9 viscosity and this would be good because your motor does not have tight bearing clearances as it's a 1970s block. The higher HTHS will protect it at elevated temperature ranges and the viscosity is thick enough for that block bearing clearance. Change it every six to eight track days and do some oil analysis and you should be fine. You didn't mention if that car had an oil temperature and pressure gauge but those would be excellent to have. Most modern well engineered oils have plenty of additives so you probably don't need the ZDDP in the track car because changing the oil more frequently is more important than extra additives. Have fun with your track season in 2024
In reply to russelljones48 :
And then as a follow-up as to how to use the oil analysis let's say we take that 13.9 viscosity oil and you get the analysis returned and the viscosity is 9.9. That's kind of a large drop so you might want to move to a 10w40. If it drops to 11.5 and your oil temp runs around 260 and then the next time you analyze it it drops to 9.7 and your oil temps were 290 then maybe you need an oil cooler. And then on the very weird chance that you are evaporating oil and the viscosity returns as a 15.5 at 100° C then you need an oil cooler. Hope that helps. Have fun.
My corolla has been running anywhere from 240⁰-270⁰ on track with 0w20 (originally 0w16). I do wonder how thick of an oil I can get away with.
In reply to PlutoE210 :
For an M20-series engine, maybe 0w30 or 5w30 at most, these viscosities are already beyond the factory recommendation but people have run them without any problems.
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