Wet Sump Oiling

Wet Sump Oiling
16 November 2020 60 view(s)

Wet Sump Oiling

For the most part, OEM engines rely on internal wet sump oil systems. There are a few vehicles out there using dry sump systems at the OEM level, but these are the exception, not the rule.

An OEM cast oil pump can only take a particular application so far though, and that’s when it’s time to step up with a replacement high performance pump. This is typically done during an engine overhaul or new build, though it could, in theory, be done as an upgrade to an existing engine as well. Two major players in the oil system market are Moroso Performance Products and Peterson Fluid Systems, and they will be providing us advice on what technology goes into today’s wet sump pumps, including how to determine what best suits your street/strip or drag racing application.



This wet sump pump has a shield mounted just above
the pickup to shield the pickup area from crank
windage improving oil pickup characteristics.

There are a number of reasons to run a wet sump oil system in a street or a street/strip application. From a cost perspective, a typical dry sump system will average about $3,000. This makes a wet sump system attractive to those with either a street/strip car or a budget-minded build. Wet sump systems including the pump, pickup, and pan, typically run anywhere from a few hundred dollars up to $1,500. Weight and complexity are reasons many enthusiasts choose a wet sump. A wet sump system is comprised of fewer parts than a dry sump, reducing weight. Fewer components also reduce complexity, simplifying the setup and maintenance for many owners. "Packaging ranks right up there with customer requests — a wet sump system can be contained within the oil pan," says Thor Schroeder of Moroso. Some street car drag racing classes also specifically prohibit the use of a dry sump system. Some will go as far as regulating the type of pan that each car can utilize. This is yet another reason to you maybe selecting a high performance wet sump oil pump.



There have been many improvements made to high performance wet sump oil systems through the years, and offerings have increased to allow for a wider variety of systems to match an engine’s needs.

Moroso offers separate oil pumps and pickups. They also offer their wet sump pumps with the pickup tube already welded to the pump, providing the engine will be using a Moroso oil pan compatible with this particular pump. By welding the pickup tube to the pump ahead of time for a specific oil pan, engine builders or enthusiasts can save some time and headache setting up the new pump and pickup at the correct height, which is usually 1/4 of an inch from the bottom of the oil pan.

Some Moroso pumps also use an inlet with a massive 3/4-inch diameter to allow for higher volumes of oil to be drawn through the pickup. Anti-cavitation slots and enlarged feeder grooves inside the pump also make sure that the pump does not starve, and that the pump gears are continually lubricated. This increases pump life, as well as engine life.

All of Moroso’s high performance cast wet sump pumps are built using the company’s proprietary casting process, which they claim increases reliability and durability. Some pumps also feature extended drive and idler shafts, which helps prevent shaft deflection, ensuring they operate properly under various load conditions. On these types of applications, the bottom cover is doweled so that the extended shafts can be properly located. Some applications also have a threaded plug to block the bypass spring, further improving oil pump performance.


A line of blueprinted cast pumps is also available from Moroso. These pumps were developed in conjunction with several high level engine builders, and feature tight tolerances and more consistent performance. With blueprinted pumps the anti-cavitation slots and feeder grooves are ball milled, ensuring steady oil flow to each side of the gears, even at high rpm, further reducing cavitation.

Since many racing engines still rely on a distributor to drive the oil pump, spark scatter can be a concern with high performance oil pumps. Spark scatter occurs when there is an uneven load placed on the distributor due to the oil pump drive. This can occur because of pump gear chatter. Pump gear chatter occurs when the pump is not designed to keep up with the demand of the engine or is cavitating and the pump gears are not being properly lubricating. By designing the pump drive gears to closer tolerances and incorporating measures to prevent cavitation, spark scatter is virtually eliminated.


"Our billet aluminum pumps are for customers who demand more out of an oil pump," says Schroeder. These pumps are constructed from 6061 T-6 aluminum, which is stronger per pound than the standard cast steel pumps. They also have none of the porosity issues that are typically associated with cast pumps. These pumps are lightweight, coming in a full pound less than a comparable cast pump. They feature a mounting boss that is three times larger than most traditional pumps, along with a larger inlet area to prevent cavitation. The billet machined housing won’t break or fracture as some cast housings are prone to. They also incorporate Moroso’s spur gear technology.

Moroso Billet wet sump oil pumps offer precision machining, along with increased strength and none of the porosity issues sometimes associated with cast pumps.



A variant of Peterson’s R4 dry sump pump, this external
wet sump pump features a twisted rotor design with
four lobes. Having the pump mounted externally can
decrease heat, as well as allow for better fine tuning of
oil pressure and volume.

Many people aren’t aware that there is an alternative to an exclusively internal wet sump oil system. Peterson Fluid Systems and Moroso both offer a single stage pump closely related to their dry sump technology, that works as an external wet sump oil pump. Technically this is still a wet sump design since the oil still stored in the pan. “You can design the pan better, so the oil will stay around the pickup in the pan,” says Wade Moon of Peterson Fluid Systems. This presents a unique advantage in many applications where g-forces greatly affect oil in the pan, moving it around. Since the pump is external, the pickup location is not as influenced by the pump location. This means the pickup can be placed in an ideal location, for example in drag racing applications as close to the rear of the pan as possible. Another advantage to an external pump is that the windage tray can be designed to run the full length of the crankshaft, allowing it to work better. The external wet sump pump from Peterson Fluid Systems features a rotor with four twisted lobes for smooth consistent operation. Enthusiasts with an externally mounted pump have easy access to the pump to fine tune it’s operation. This allows oil pressure and flow rates to be tailored to the engine specifics. An external wet sump pump system offers far less complexity and weight than a dry sump, and can typically be bought for about half the cost of a dry sump system for the same engine.



Like anything, there are disadvantages to a wet sump system. "Standard cast oil pumps are great for production cars but they’re reaching their limitations in a race setting," says Schroeder. Moon points out in a drag racing situation, having oil in the crankcase is still going to cause windage at launch, "No matter what you do in a wet sump system, when you launch, oil is going to get into the rotating assembly, which is like putting it in a blender, it causes aeration." Wet sump systems also build up more heat because the oil is stored inside the engine.

If an engine is running a vacuum pump, then the oil pump must work to overcome that vacuum in order to draw in oil. This can be more difficult in a wet sump system since, unlike in a dry sump, the vacuum pump in a wet sump is competing for the oil, pulling it away from the pickup rather than scavenging it back to the reservoir like it would in a dry sump.


"There is a mentality that it’s just an oil pump and oil pan, but the oil is the lifeblood of the engine and these components have a very important role," says Schroeder. What he is hitting on is that how the engine is lubricated should be taken into consideration as part of the build process. Much like a fuel system works best with closely matched components, so does an oiling system.

Left: Compared with a dry sump system (pictured right), a wet sump system offers simplicity, tight packaging, and low cost.


Oil pans are an area that can have a major impact on the performance of a wet sump system. Larger capacity pans are ideal, but may not be practical in all street-going applications or legal in all racing classes.

Kick-outs can help with ground clearance when they are compatible with other components. According to both Moroso and Peterson Fluid Systems, the pan should be designed to work in conjunction with the oil pump and pickup. The pan should trap oil close to the pickup and keep as much of it there as possible under all conditions.

The entire oil system should be considered when planning an engine build or upgrade. This includes the pump, pickup, pan, windage tray, coolers, and accumulators.


Windage Trays

If you plan to run an external wet sump, you’ll need a
pickup similar to this one to place in your oil pan.

Like oil pans, if they’re legal for the class, a windage tray is a valuable tool for helping move excess oil away from the crank. Windage trays must be compatible with the pump and pickup being used. In using an entirely internal setup, the windage tray can not run the full length of the crank. This must be taken into account when ordering, building or designing one.

The pickup must be matched in diameter to the oil pump inlet. It must also be located approximately a 1/4-inch from the bottom of the pan. The pickup tube should provide adequate flow matched to the pump’s design. This will help prevent cavitation or loss of pressure.


Moroso also recommends an oil accumulator as a reasonable safeguard if you’re racing a car that’s required to run a wet sump system. It’s also helpful on street cars. Accumulators help reduce engine wear by keeping a charge of reserve oil that is automatically distributed when a pressure drop occurs, as well as allowing for priming of the oil system at startup.

An oil accumulator can be an engine’s life saver in the event of a sudden drop in oil pressure. It can also reduce wear caused during startup by pre-lubing the engine.


In spite of some disadvantages, wet sump oil pumps are still the most widely used pumps in both racing and OEM high performance engines. Whether rules, packaging, budget, or convenience require them to be used, for many applications they can provide proper oiling performance. When coupled with matching components, a high performance wet sump oil system can help ensure long engine and component life even under the harsh circumstances of a racing environment.


This article is courtesy of Street Muscle Magazine
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