Wet or Dry Sump?
The Answer is Science, Not Art
You may have heard the analogy that the oil pump is the heart of the engine – as the heart pumps blood to keep us alive, the oil pump moves oil throughout the engine. A failure of either “heart” to pump its fluid properly will quickly be catastrophic.
Yet every heart is basically the same size, in pretty much the same place and functions virtually identically to every other heart in human history. Contrast that with the heart of today’s performance engines and it’s a surprise that engine builders don’t receive the same respect and bank accounts as their cardiac brethren.
Wet sump? Dry Sump? Customer preference? Sanctioning body restrictions? There can be great confusion about what oiling system is the best. Of course, as with any engine-related component the word “best” is impossible to define. “Appropriate” should instead be used, because there are multiple factors that must be considered when specifying the best system for any application.
Depending on the application (racing, marine, diesel, stock), engine rpm and budget, deliberate conversations with your customer can answer most of your questions to determine which lubricating system is right for their needs.
It’s not a simple decision or one to take lightly. It often requires collaboration and agreement – or at least understanding between both you and your customer. High-end components and machine work deserve the best chance to live.
Remember, “saving money” on the oiling system by selecting something inadequate is a poor short-term and potentially deadly long-term decision. The oiling system should never be an afterthought. It’s the key to protecting the other components and keeping them lubricated.
So how do you decide? “Trial and error used to be the determining factor,” explains Steven Hogue, champion race engine builder from Akron, IN. “My dad would call it ‘back in the old days,’ but today, a lot of companies can do the testing and technology research for you. You can look anywhere and find data now, but of course you sometimes have to be careful what you consider “facts.”
Hogue says he relies on a network of other experts – manufacturers and engine builders – to help answer questions he may have. “We have a reliable network of business friends to bounce ideas off of to see what they are using or what kind of issues they’re having or might have had with other manufacturers. I can honestly say that our group is very open and friendly about a lot of things. Everybody has their niche for something special and there’s plenty of work out there for everyone to share, and everyone we deal with knows we can all learn something from someone else.”
Hogue and his father Bruce have decades of experience between them, an experience factor that is rarely lost on customers. “Depending on the application the engine is going to be used for we have a baseline of what we plan on putting in or installing on that engine. That’s where it becomes very important to have a good relationship with your customer – if the customer cannot tell us exactly what they want to do or what the expectations are for the engine, it doesn’t do us any good to give a recommendation,” says Hogue.
Randy Malik, of RM Competition also calls on his experience when specifying engine systems. “I started off in competition doing the drag race thing for myself and a partner in Super Stock around 1970, learning first how to make the horsepower; then went on to the asphalt oval track in Late Models around 1982 to 1989 (to learn how to make that good horsepower live a long time); which gave me a desire to turn the car both left and right, so road racing in the GT-1 class in SCCA got my attention for the next 16 years,” he says.
“Now I use all that gained knowledge from all these sources when building my customers’ engines to the best of my know-how, using the latest proven techniques mixed with ‘old school’ reinforcements while giving my expertise in the component selection and doing modifications for my customers,” Malik explains. “They get all they can ask for (and learn about some things they could never dream they would actually need to be competitive).”
For Malik, the question of who selects the engine oil system is simple. “The customer has absolutely NO input on what oil pump gets put in his engine. If he won’t trust that he will get the correct one for the application, he can get his engine built elsewhere. It is MY name on the end product!”
Lubrication systems for internal combustion engines on passenger vehicles may be wet or dry sump-based systems. A wet sump lubrication system is typically used on production vehicles. Lubricant is stored beneath the crankshaft and oil pan. The oil pan needs to be large and deep in order to hold sufficient amounts of oil to lubricate the engine.
A stock wet sump oiling system with a stock oil pump and stock oil is unlikely to be good enough for any performance engine, experts caution. If an engine is being built to rev higher, make more power and accelerate a vehicle faster, you’ll definitely want to upgrade the oiling system.
But it’s not just higher rpm that should get your attention, however. How the engine will be moving in space – the X, Y and Z geometric axes – will dictate changes as well. Acceleration, deceleration and body roll can cause oil in the pan to slosh, often to the extent that the oil pickup starts to suck air, which leads to a sudden and dangerous drop in oil pressure. If the situation isn’t remedied almost immediately, it can ruin the rod and main bearings.
Street Performance Recommendations
Street performance may not seem all that demanding, but it can be the equivalent of drag racing or road racing depending on what’s happening at any given time. Most stock oil pans can handle “normal” acceleration, deceleration and cornering forces without starving the pump. But as those G-forces in any direction go up, so do the chances of sucking air into the oil pump’s pickup.
A common upgrade for a wet sump system is replacing the stock oil pan with a higher quality aftermarket performance oil pan. Performance pans have better baffling to reduce oil slosh so the pickup will stay submerged in oil. A deeper sump can help increase total oil capacity, which helps the oil run cooler and last longer – of course, space limitations may prevent this from being an option.
A road race pan with baffles and trap doors can limit oil movement in all four directions and some type of windage tray or scraper will help keep oil away from the crankshaft. A windage tray will reduce drag on the crankshaft and oil aeration, both of which are good for making more power and improving lubrication.
Stock pumps can usually provide adequate oil pressure for engines that won’t turn more than 6,500 rpm, but if it has high mileage and potential internal wear issues, it probably won’t be up to the engine’s rpm potential. There are many different performance aftermarket pump designs. Ones engineered to flow more oil and to maintain pressure at higher engine speeds, and ones available for upgrade consideration, so do your homework.
“EVERYTHING about the engine determines what oil pump to use,” says Malik. “A street/strip engine requires different parameters than a high rpm race engine. A high-torque, lower rpm race engine with wider bearing clearances will surely need to use something even different.
“A street/strip engine needs more pressure at lower cruising rpm where a race engine is very happy with no more than 12 pounds per 1,000 rpm; less if the bearing clearances warrant it.”
Dry Sump Systems
Another option to success in high G-force applications involves converting the engine to a dry sump oiling system. Dry sump systems are most commonly found in ultra-high performance applications like NASCAR, F1, Le Mans and Pro Stock drag racing, but are also found in heavy diesels and some passenger cars like the Corvette Z06, Porsche 911 GT3 and Mercedes AMG GTS.
Dry sump lubrication systems utilize an external tank to store some of the oil outside of the engine, meaning the large and deep oil pan found in a wet sump system isn’t needed. The engine can be placed lower in the vehicle, often improving handling characteristics.
Oil is pumped from the external oil tank or reservoir to the engine components that require lubrication. Oil thrown from the main bearings during engine operation drains to the sump located in a lower part of the crank case, then pumped back to the oil tank by one or more scavenge pumps. The pump or pumps route the oil to an external storage tank, which may hold anywhere from one to five or more gallons of oil. The external tank serves as a reservoir and allows air to separate from the oil. A vent allows air to escape.
To push the oil back into the engine, a dry sump system uses an external pressure pump, which is usually mounted in the same stack as the scavenge pumps (all share a common driveshaft that runs down the middle of the assembly). The pump’s output is routed directly to the engine’s crankshaft bearings with hose fittings and an adapter that fits over the old spin-oil filter mount, but some of the oil can also be routed through a valve block or manifold to provide lubrication direct to the valvetrain and/or turbocharger.
The dry sump pumps are usually mounted on the side of the engine and driven with a cogged belt off the crank pulley. On some applications (sprint cars, for example), the pump assembly may be mounted on the front timing cover and are driven off the cam.
Additional components that may be used in a dry sump oil system include an external remote mounted oil filter and/or inline oil filter screens, an engine oil cooler (a must for endurance racing), a control valve for adjusting oil pressure and flow, possibly an oil pressure accumulator (which helps with engine and turbo cool down after shut down, and helps prevent dry starts), and lots of plumbing and fittings (usually -10, -12 and/or -16 hoses and fittings).
Dry sump oil systems are not cheap, and can cost from $1,800 to $2,500 or more depending on the setup used. Some high-end billet pumps can cost thousands of dollars, and custom tanks can be expensive to fabricate. Dry sump oil pans and setups are available for a wide variety of engines, even four cylinders and V6s, both domestic and import.
Of course, if the pump is the heart, then oil is the blood. Hogue says, “You must have a pump to pump it but it doesn’t do any good if the blood is no good. The oil is kind of like a carburetor or air filter for our customers. Each racer seems to have his own opinion on what they think is best, but we will always give our recommendation of the oil we suggest will work the best.”
Hogue says all of his engines, depending on application, leave with the same amount of rod, main, lifter and cam bearing clearance. “We bring pressure up before the engine leaves the shop and every wet sump engine leaves with the same brand of motor oil we choose to put in there.”
After changing the oil initially, the customer will often install a different brand and viscosity of oil. “That’s a customer preference,” says Hogue. “But when we go to tear the engine down for a rebuild, if something looks a little different in regard to bearing wear or sludge in the bottom of the pan, we’ll take photos and then contact the customer asking what brand of oil they were using and whether they were changing the oil hot and regularly.”
Hogue says that while some of his customers say, “Well it didn’t blow up, so why do I need to change?” More of them recognize the importance of maintaining their oiling system. “After seeing pictures, some of our customers have actually started changing their oil hot or even switched oil brands. It’s an everybody wins situation.” ν