Even if your pickup is in the oil, the oil is often like a bottle of soda that was just opened. The oil splashes around, gets churned by the crankshaft and even with windage trays etc, it will aerate read: foam. With a dry sump system, the oil is returned to the tank where it has a chance to deaerate and get picked up from the bottom. You also have the opportunity to help it do that with inline devices.
The best one of these is the Spintric from ARE , which is like a centrifuge for the oil. As the oil passes through, the momentum of it going around in a spiral squeezes the fluid to the outside while the gas escapes from the middle.
This is especially important on a dry sump system because it evacuates a lot more than just the oil. And that leads me to another benefit which is most poorly understood.
A wet sump depends on gravity to return the oil back into the container. A dry sump system needs a way to transport the oil from the engine to the tank and back. Enter the dry sump oil pump. It sucks oil from the tank ideally not doing a lot of work to do this, more on that in the details of my install and jams it into the motor under pressure. Here we find another benefit of dry sump where you can adjust this external oil pump to set the pressure to whatever you desire without taking anything apart.
But the same pump also sucks the oil out of the engine to deliver it back to the tank. The dry sump oil pan seems like it is a non-factor — just a plate of aluminum you need to bolt up to cover up the crankcase.
ARE makes pans based on 40 years of experience , which optimize the oil return via mini-sumps with baffles and screened pickups. So now that you have the pump sucking the oil out, what else good does this do? Well, why do we need crankcase ventilation?
Because combustion gases will invariably find their way past the pistons, and the higher performing the engine, especially with forced induction, the more blow-by there will be. The blow-by will mix with oil vapour and need to be evacuated. Modern emissions systems will pump it back into the intake to be combusted or in modern Direct Injection engines, cake onto the intake valves, thanks a lot… and many high performance projects will instead redirect this mixture into a catch can or dump it out of a hose onto the ground… tsk tsk , where they will periodically need to drain the accumulated condensed oil and water.
But imagine if instead of the crankcase being pressurized, it was under vacuum. This tells me that I want three stages, at minimum. The first, and most common is the gear type. This is composed of two or more gears that mesh together in such a way as to create pockets which trap air and oil. As the gears rotate, the fluid that is trapped is pressurized and moved from one part of the pump to another. Because this type of pump traps less air, it is more efficient.
The second type of scavenge stage is Roots. In this design, instead of gears, we have spinning rotors that trap air and oil between the rotors, pressuring them and moving them further along the system.
The Roots type scavenger pump pushes more volume, but it also traps more air, thus decreasing efficiency. I prefer to utilize a pump with a mix of both gear type and Roots stages. This way I get the best of both worlds. I increase volume using the Roots stage and I increase efficiency using the gear stage or stages. Every engine, no matter how much care you take of it, generates some form of debris. This is carried away by the oil and hopefully trapped in the filter or filters.
This debris causes damage throughout the engine, and the oil pump is no exception. To cut down on the amount of debris floating in the engine, besides the magnets I mentioned above, dry sump pumps have filters in the scavenge tubes, this helps keep the worst of the debris from damaging the pump.
Roots-type pumps are somewhat fragile and susceptible to damage caused by debris floating around in the oil. Gear-type pumps are far less susceptible to damage by debris. Every pump will have listed on its spec sheet the ideal RPM range, after which the pump will begin losing efficiency due to cavitation-the creation of air bubbles in the oil being pumped. The pans capacity can range from 3 quarts to 20 quarts or more, depending on the engine.
The oil is sucked up a pickup tube into the stock oil pump, where it is filtered and supplied to the engine under pressure. While this system is very adequate for highway use, it presents problems under racing conditions. Aside from the size of the pan, and necessity of a deep sump, the oil is subjected to extreme cornering forces in racing, and the oil simply "crawls" up the sides of the pan and away from the pick-up.
Although there are many good designs, with trap doors, etc. Aside from the obvious pressure loss, this also results in a reduction in horsepower as well as oil aeration. These are the reasons dry sumps were developed.
I will discuss other advantages later.
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