Let’s face it, the days of just choosing you favorite brand 20W-50 and putting it in your muscle car, race car, and lawn tractor are over. While each engine is a four-stroke, the engines themselves and the motor oils are more specialized. So that means you have decide which oil is right for your muscle car, which oil you will use in your race car, and what oil you will use in your lawn tractor.
The key to selecting the right oil for any application is matching up how the engine is used with oil chemistry for that type of use. Back to your lawn tractor. If you are just cutting grass, the factory recommended oil is just fine, but if you are drag racing the lawn mower, please remove the blade! And while you are at it, drain the oil and put in some racing oil.
You see, how the engine runs determines what type of oil to use.
A car that makes a short drive to work 5 days a week needs more TBN than a race car that runs 50 laps each weekend. What is TBN you ask? TBN stands for Total Base Number, and it measures how much acid neutralizing power is in the oil. You may not realize it, but corrosive wear is one of the major forms of wear in your engine. In fact, one of the main reasons for increased engine life today has been the reduction in corrosive wear. That’s right, many older engines did not wear out -- they corroded.
Short trip driving is the worst for producing engine killing acids. Water is a by-product of combustion, so some water vapor always makes it way into the crankcase of your engine. If the engine does not run long enough to get warm enough to evaporate the water vapor out of the engine, the water vapor builds up. When the engine cools down, the water vapor condensates, and now you have water in your engine. The water mixes with the sulfur in the oil and the partially burnt fuel to create a very corrosive chemical cocktail.
To fight this, oil engineers have developed detergent and dispersant additives to fight corrosion. The power of the additives relates to the TBN value of the oil. A very strong detergent and dispersant package will have a high TBN value, and that signifies an oil that is good for frequent short trip driving.
OK, so why not use a high TBN oil in my race car?
Simply put, the harder the engine runs, the less TBN your engine needs. That may seem counter-intuitive, but it actually makes sense when you know that Detergents and Dispersant compete against the Zinc anti-wear additives and EP extreme pressure additives your race engine needs.
Nobody building a race engine lowers compression ratio, installs lighter springs and a smaller cam to make a production engine into a race motor. Nope, you do the opposite, and when you do, you increase all the contact pressures in the engine. The increased pressures and loads in the engine need extra anti-wear protection, so the oil engineers add more anti-wear additives like “zinc” (ZDDP, ZDP or ZDTP) and EP extreme pressure additives like Molybdenum and Sulfur. These anti-wear and EP additives form sacrificial films that protect your race engine from adhesive wear due to the higher loads in a race engine. Anti-wear additives and EP additives like ZDP and Molybdenum Disulfide act like armor to shield your engine parts from adhesive wear.
The Detergents and Dispersants that fight corrosive wear are trying to strip that armor off your engine parts. All of these additives are needed to protect your engine. The key is selecting the right balance for your engine.
While race oils provide more anti-wear and EP additives to fight adhesive wear, the lower level of Detergent and Dispersant require more frequent oil changes to control corrosive wear.
Since a daily driver is more prone to corrosive wear, the right oil for your daily driver needs a higher level of Detergents and Dispersants, and the engine in your daily driver is built with smaller camshafts and lighter valvesprings that safely run on lower levels of anti-wear additives.
When you have an older muscle car that does short trip driving and sees extended periods of sitting in a garage, you need a higher TBN oil to protect against corrosive damage. However, many older muscle cars also have “old school” push rod valve trains and good sounding camshafts. Now what do you do? Don’t worry, the oil engineers have found the right balance of increased anti-wear additives and TBN for your hot rod -- enough ZDP for your camshaft and enough TBN to protect your engine during winter storage.
So what about that drag racing lawn tractor? Use a racing oil, and keep a good eye on the oil. Drag racing is combination of the worst of both daily driving and racing -- short trips, low temperature and really high loads. The best recipe for low adhesive wear and low corrosive wear in a drag racing engine is to use a high quality racing oil and change it often. Again, keep a close eye on the oil. As long as the oil looks good and smells normal, the oil is good. If the oil turns dark, begins to smell like fuel or turns milky, change the oil. These are all signs of fuel dilution and chemical attack on the oil, so the best defense for your engine is to send in fresh troops with the correct weapons to protect your engine for the way you use your engine.
I know this process takes a little more thought and work, since engines, especially race engines, cost a lot of money, spending a little extra time and money on your oil program will more than pay off in extended engine life.