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Performance Oils and Additives: Got Zinc?

Experts say it may be time to change your motor oil (brand). It’s more than a coincidence that engine builders have experienced more flat tappet cam failures in the last few years than at any point prior.

By Brendan Baker

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How do you choose the right oil for your racing or performance engine application? While you don’t have to be a chemist to know there are differences in oil formulations, these variations can be as broad as the type of oil, or as specific as the additive package that is used.

Your father’s motor oil may have been old reliable, but it may be time to move on. It’s more than a coincidence that engine builders have experienced more flat tappet cam failures in the last few years than at any point prior. And that’s because today’s engine oil has a lower amount of anti-wear additives than your flat tappet cam requires in order to keep it spinning freely.

Experts say that the reasons behind the changes in engine oil are numerous, but one of the main reasons is that the American Petroleum Institute (API) has regulated the amount of zinc levels to .08 percent, down from .15 of a few years ago (and even higher levels before that) due to its harmful effects on catalytic converters and emissions systems.

The latest API formulations are aimed at extending the life of catalytic converters not racing engines. Around 1996 most of the OEMs had already started manufacturing OHC engines with roller followers, that in turn, allowed them to use lower zinc-phosphorous anti-wear additives.

So while performance engines of the early 1990’s could share the same oil as production engines without consequence, today, the use of API approved street oils in many performance applications will likely lead to trouble, especially during flat tappet cam break-in periods.

Just what exactly is your oil made of? To help regulate the formulations and performance of the many types of oil, the American Petroleum Institute created a system of classification for base oil types. The majority of each bottle of motor oil is made up of a base-stock taken from one or more of five categories, or groups. Group I base stock is the least refined base oil from crude oil; these are most often utilized in straight-weight, conventional motor oils. Group II base stock is more refined than Group I to remove more impurities and improve its properties as a lubricant. Group II stock is often used when creating many of today's multigrade conventional motor oils. Group III base stock is refined to the point that it will perform at the levels of any other synthetic base stock and hence it is called a synthetic. Group IV base stocks are PAOs (Polyalphaolefin) or historical synthetics and Group V is essentially anything that will not fit into the previous four categories such as esters and polyolesters.

While one or more of the base oil groups make-up roughly 80-85% percent of the motor oil, the remaining percentage comes from a combination of additives. The additive package can be any specific mix of viscosity modifiers, anti-oxidants, anti-wear additives, dispersants or more; with each component responsible for at least one separate task. The viscosity modifiers are used to help keep multigrade motor oil within the desired viscosity range as the motor oil heats up or cools down. Anti-oxidants are used in the motor oil to help the oil cope with the high temperature extremes inside the engine. The anti-wear additives assist in lubricating the moving components, and the dispersants keep the impurities in the engine oil in suspension so they can be safely removed by the oil filter before the oil travels to critical components of the motor. It is the delicate combination and mixture of each of these components in the additive package and the base oil selection that truly determine the quality of the each quart of oil.

Experts say that the additives in API blends will no longer cut it in a racing or performance engine. There is no denying that API oils for the most part work very well in late model engines where there are roller cams and much less friction than in high powered racing engines, which are in many cases, good old pushrod V8s.

According to Lake Speed, Jr. of Joe Gibbs Driven Racing Oil, one of the important differences between racing oil and API oil is the limited amount of phosphorous in API blends. The EPA limits the amount of phosphorous and zinc, specifically it’s the phosphorous, not the zinc that is limited. Phosphorous is a component of Zinc dialkyl dithio phosphate (ZDDP, or ZDP) is a family of zinc salts of dithio organophosphates. And they easily dissolve in mineral and synthetic oils that are used as lubricants.

Zinc phosphate is mainly for anti-wear. The zinc and phosphate go hand and hand. So when you limit phosphate you limit zinc as well.

“You can put zinc in the oil but it won’t act as an anti-wear agent until you add the phosphorous,” says Speed. “When you have a limit on the amount of zinc-phosphorous you limit the anti-wear agents. The combination of zinc and phosphorous is limited to a maximum of 800 parts per million in API/SM classification, which is the latest classification that came out in 2004.

“Any oil that you get that says API or ILSAC GF-4 contains a limited amount of zinc and phosphorous, and for most racing applications, that’s not what you want,” says Speed.

It is for this reason some engine builders have switched to diesel oil for break-ins as some of these formulations are known to have higher levels of zinc.
“The current diesel oil spec is CJ-4 is limited to 1,200 parts per million (ppm), so it does have 400 ppm more than API pass car oil but it’s only marginally better. A lot of people get mislead hunting down the oil with the highest ppm, as if it were the Holy Grail, and it really isn’t,” says Speed.

The amount of detergents and the balance to the amount of detergents and anti-wear is another big difference between racing oil and API oil, say experts.
Detergents are the additives that clean the sludge and build up in the engine. And those are keys for passenger car engines that operate in short spurts and at lower operating temperatures. The oil is typically not hot enough to vaporize any of the contaminants, which attacks the oil and creates more issues so that you need acid neutralizers and so on. That’s all compounded in a passenger car by the fact that you’ve also got EGR to contend with. So EGR is dumping more fuel and contaminants back into the engine, which just makes the situation worse. Manufacturers then have to formulate passenger car oil for that kind of environment. And by and large these oils do a great job for the environment they operate in.

Let’s take a look at some different types of performance oil. Some are racing formulations and others are API blends for street performance applications. Choosing the right oil for your performance application comes down to a number of things including temperature, load and rpm range. These are the most important factors.