It has been said that racing is all about control. What you need to control depends on who you're talking to and what you're talking about. For some racers, controlling the oil system is rather simple-a matter of merely making sure you have enough oil in the engine to make the race. For others, it may be about how you control the oil once it's in the engine.
Making sure there's enough oil in the engine is a fairly simple task. We need to look at it from a systemic perspective because that is what we're dealing with, a system. There are multiple components that make up the oil system. If one of them fails, the whole system will be brought down and your engine will blow up in your wallet.
We are discussing control, and racers, being the control freaks they are, always look for ways to improve the performance of their engines. We know that horsepower can be gained through the use of different viscosities of oil in the engine. But is there power in further control of the oil?
In the oil systems of most passenger cars, there is a a sump below the engine. We call it the oil pan, hence the name wet sump. The oil pump pickup is located in the lowest portion of the pan, and the pickup feeds the oil pump, which moves the oil from the pan into the engine, where it is routed through the oil filter and then through the various oil passages drilled into the block. Once the oil reaches the various bearings, lifters, and other portions of the engine that require lubrication, the oil flows back into the pan, where the trip starts all over. While this is an oversimplification of the process, this is what is happening while the engine is running. There are several other dynamics occurring at the same time the lubrication process is taking place.
On the track, your oil system is probably working harder than it needs to, but that's the nature of this beast. It's possible that the oil pump is pumping too much oil to some parts of the engine and not enough to others. This condition is wasting horsepower. Many times the oil does not run back into the pan fast enough, and oil could be pooling in the heads and lifter valley. This can cause oil starvation at the pump pickup. Not to mention the g-forces caused by driving the car around the track can force the oil, that makes it back to the pan, away from the pump pickup.
The oil being pumped to the crank and rods does not fall away from the crank or the rods while the engine is running at high speeds. The oil forms a taffy-like blob that sticks to the crankshaft and rods, and this causes a real problem. It takes a good bit of power to drive this blob of oil through, and the oil becomes aerated. The entry of air into the oil is a very bad thing, as it causes a loss of lubricity. The oil that is going into the pump now has a high quantity of air mixed in, and air is not known for superior lubricating quality. It also heats up the oil, which is another bad thing.
Note the different types of gears in these two scavenger pumps. The pump on the right uses a Roots type of pump in the scavenge side.
This blob or mass of oil trapped around the crankshaft, the result of the engine running at high speeds, starves the engine of oil. We find high engine speeds at the end of the straight, where the engine is at its highest load and has been operating at high rpm for an extended period of time. So we have a multiple whammy in that the protection the oil provides is not there when the engine needs it. The engine is running at maximum rpm and load, and the oil could be pooling in the heads and lifter valley or stuck to the crankshaft and rods. This happens for several reasons:
* The drain passages in the block and the heads are not large enough.
* The g-forces generated by racing are not allowing the oil to easily drain back into the sump.
* Too much oil is being pumped into areas where not as much may be needed.
* Oil is trapped in the spinning crank and rod assembly due to windage issues.
This can amount to several quarts of oil in the upper end of the engine and several more stuck to the crank and rods. In a 5- or 6-quart system, that doesn't leave much margin for lubrication. The crank and rods are covered in this blob of oil that is being whipped up until it has the consistency of brown Cool Whip. So when the engine needs oil the most, it is not in the pan where the pump can pick it up and move it back to the bearings and other sliding surfaces.
The wet sump system that works so well on your passenger car is marginal at best in you race car. If the power levels do not exceed a range of 350 to 400 hp, this is not a real issue. As the power level in the engine starts to reach 1.7 to 2.0 horsepower per cubic inch, the wet sump system becomes a liability. In fact, with a wet sump system, it will be difficult to maintain those kinds of power levels on the racetrack for long intervals of time
A Better Way
The aerospace industry provided the solution to a racer's problem. During the time period that airplane engines were being developed (the '30s and '40s), it was clear that a wet sump automotive-style oil system would not be robust enough to survive aircraft use. Keeping the oil in a tank separate from the engine was the only real answer. This required a different type of oil system, one with multiple pickups at various points on the engine to pull the oil out of the engine and back to the pump. The pump was also different, as it had multiple stages for removing or scavenging oil from the engine and a pressure stage for supplying pressurized oil to the engine. Problem solved. Again, I have oversimplified the situation, but it paints a clearer picture.
Dry sumps may have their roots in the aerospace industry, but they are very common on high-horsepower racing engines and on some high-performance street cars. The conversion from wet sump to dry sump is not that complex. All the parts you need are available from many different racing vendors. There are probably 15 to 20 different manufacturers of dry sump pumps that service the racing market.