Film Strength

We mentioned earlier that race engines produce a lot of heat, and that's no surprise. But it does create a pretty significant hurdle for performance oil manufacturers. Racers want to be able to run the thinnest oil possible to reduce parasitic horsepower losses, but just because they use a 10W-30 oil (or lighter) that doesn't mean they are going to go any easier on their engine on race day. Thinner oils means tighter bearing clearances are required, so the oil that is providing the cushion between the crankshaft's main and rod journals and the bearings stay just a little bit longer and the oil temp in that area can be quite a bit higher than what you are seeing on your gauge.

The constant battle with racing oil is to make sure it can still provide adequate protection at extremely high temperatures. And when we are talking about protecting the bearings, we're talking about film strength.

"When it comes to the bearings, the one that gets worked the hardest is the bearing shell in the top side of the rod," Groom explains. "The reason is because when that cylinder first fires, that's where that force is going. (The spark plug fires the air/fuel charge before the piston reaches TDC, so combustion pressure is initially pressing down on the piston and rod while it is still travelling up in the bore.) Everything in that engine is depending on a very thin film of oil. And if the engine fires so hard that it is able to compromise the strength of that film, then pieces of metal start touching and that's the beginning of an engine failure. You want the oil to have enough strength to be able to withstand those forces so that you maintain what is known as hydrodynamic lubrication, and the crank's main and rod journals and the bearings never actually touch.

"A lot of oils, when you heat them up they thin out and the film strength goes away," he continues. "When that happens the parts get dangerously close to touching, and then the heat snowballs and goes out of control. But if you can get the oil to maintain its film strength under extreme heat, then everything tends to level out.

"A good indicator of that is when you get out of the throttle at the end of the straight going into the corner, the oil pressure gauge doesn't lay over to zero. We've worked very hard to produce a line of oils that maintains its film strength at all costs. I've seen our oils in situations where we are at 330 degrees on the cold side of the dry sump pump. That's hot, and it is still maintaining pressure, so that's really good."

Oil Analysis

While speaking with Groom, he continually referenced what he was able to learn from performing oil analysis from different race cars. For example, he helped one race team determine exactly how long it could safely go between oil changes given the specifics of the track conditions and engine it was running. The team was able to save money by extending its oil change interval while still having confidence that its engine was properly protected. We asked Groom how regular teams could achieve the same thing even if they don't have access to high-tech analysis like the oil manufacturers. To our surprise, Groom says that AMSOIL offers its oil analysis services to anyone who wants to take advantage of it.

"That's something that we probably don't make enough people aware of," he says, "but we do offer it, and it can be very helpful to a lot of teams. Oil analysis is something that most racers under-utilize because they change their oil so often, but I can tell you through oil analysis how much fuel they are putting past the rings. I can tell you if the air filter is loose. Because as soon as you get a little sand in the engine the iron number goes up in the oil. Racers by and large hate to spend money on oil, so they are always asking ‘how long can I go before I have to change it?' And how long you can safely go--especially when you are racing on dirt--depends on a few very important factors. Number one is the air filter, number two is the fuel getting into the oil, and number three is the quality of the oil itself.

"I can tell you, for example, by doing an oil analysis if the air filter isn't sealed tightly and is letting dirt or sand into the engine. That's because the amount of iron in the oil will go up real fast. That's the grit getting past your air filter wearing your cylinder liners and your rings. And if fuel is getting past the rings, then the fuel level in the oil goes up. When that happens it reduces the viscosity of the oil, and that means your protection level is going down. "Those are just a few of the things you can learn from doing a chemical analysis of the oil that comes out of your engine. And having an oil analysis done really isn't that hard. All a racer has to do when it drains his oil is to put some of it in a clean bottle and send it to us. AMSOIL does all of its oil analysis right on site. Racers may say that they don't need to do an oil analysis because they change their oil after every race, and that's great. But why not learn what's going on with your engine during that race? And if you can save a little money by safely extending your oil change intervals, why wouldn't you want to do that?"

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