What is Dry-Sump Oiling, and Why do Performance Cars Have it?

Porsche’s always used it, Lamborghini uses it, and the fastest Corvettes take advantage of it too. It’s a dry-sump oil system. But what does that mean, why do they use it, and how does it work?

A sump is just a pit where liquid collects. Like that hole in your basement with a pump that saves the day and keeps your old magazine collection dry when it rains really hard. An engine sump is the same thing. Only instead of in your basement, it’s at the bottom of the engine. In short, the engine’s sump is the oil pan. Especially that big lump that sticks out from the bottom of it.

That’s where the oil goes when it’s not busy lubricating your engine. It just hangs out in the pan, being all oily and doing oil things, like collect contaminants. And seep from the pan gasket.

If your engine has a big pan where the oil sits, like nearly every combustion engine ever made, it’s called a wet sump. The oil sits in the sump all the time, which makes it wet. Though we hope there’s no water in there.

Dry sump pumps and tanks

A dry-sump system doesn’t just let the oil sit there. Instead, it pumps it somewhere else. But we’ll get back to that.

A wet sump oiling system has worked very well for a very long time. You put the oil in the pan. A pump with a pickup at the bottom of the pan pumps the oil through passages in the engine to where it needs to go. Then gravity pulls it back down to the pan.

But that’s not a perfect system. If the oil takes too long to drain back down, you’re relying on the oil in the sump to last until the oil eventually returns. If it doesn’t, for whatever reason, your engine will run dry. Bang.

If you’re in a turn for a very long time, the oil can all slosh to one side of the pan. Then the pump can’t suck up enough of it and bang. There’s only so much extra oil you can store in the pan, after all. Same thing if you’re accelerating or braking for extended periods. Bang. Put too much oil in, and road motions can splash the oil up into the spinning crankshaft. That foams it up like a blender. The pump can’t pick up enough and, you guessed it, bang.

Those are all unusual situations, and until recently there weren’t all that many cars that could corner hard enough for long enough, or accelerate quickly enough for long enough, for it to be a big problem. Modern supercars, though, are absurdly fast. And they get driven on the track, where they can easily overwhelm this archaic oiling system.

Enter the dry sump.

A wet sump engine. Compare the large sump with the smaller one in the next photo

First, the name’s a bit of a misnomer. It’s not entirely dry. There’s always some oil there, and the oil still falls into the pan. But it has a much smaller volume. And instead of a pump dipping down from the engine to the inside of the pan, there are multiple pumps. Or fittings on the outside.

They’re called scavenge pumps. Because they scavenge the oil, in whatever amounts they can get, and pump it to a storage tank. The latest 911 models have four pumps, one at each corner of the pan, making sure that every drop of oil gets sucked up.

Dry sump with shorter oil pan

Where does that oil go? A tank, located somewhere in the engine compartment. Of course, since any dry sump car is a performance car, it probably goes to an oil cooler first. Or at least somewhere in the process. So the engineers designing the car can store loads of oil in a separate tank. Instead of under the engine. A high-pressure pump then moves the oil from the tank to wherever it needs to go inside the engine.

So what are the advantages? Not storing eight quarts of oil under the engine means that the engine can sit lower. Closer to the ground. For a better center of gravity and improved dynamics. That can lower the hood height, too. Making for better visibility and aero. Or making room for a supercharger on top without too much hood bulge. The tank can also be made as large as will fit underhood. More oil can mean longer between changes, better reliability (because contaminants are diluted in more oil) on track and even better cooling since there’s more oil to heat up.

The big reason, though, is that no matter how hard you corner (and for how long), there’s going to be oil in the storage tank. Which means there’s going to be oil for the engine to pump around and keep itself lubricated.

So why doesn’t every car have one? Well, adding multiple pumps, storage tanks, and hoses is expensive. If you’re not taking your car to the track, it’s not worth that cost to you and it’s not worth it to the automaker. It’s also more complex. Adding all those hoses and tanks takes up space and means more parts (and more things to go wrong).

So there’s a performance benefit to be had. Worth it for track cars like the Porsche 911 or Corvette Z06, but not worth it for straight-line monsters like Dodge’s Demon. And that’s the dump on the dry-sump oiling system.

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