Tech: Crankcase Pressure Control – Oil and Air Control

Proper control of engine crankcase pressure and oiling can be a significant advantage in terms of horsepower and engine life. While all modern factory engines are equipped with a PCV system, those factory parts seldom do enough. The original equipment system, especially on supercharged, or any modified engine is often inadequate. In nearly every case, there are advantages to properly controlling the vapors and oil that normally escapes back to the engine via the factory PCV (Positive Crankcase Ventilation) system.

Vacuum pumps are another component of the crankcase pressure solution which we will also address in this article. This is a definite area where racers can gain an advantage when allowed by the rules and guidelines set forth. Control of engine oiling is also critical in all high performance applications. By controlling and getting oil in the proper volume to all areas of the engine, parts life can be improved as well as engine performance. 

We talked with several high performance companies including Moroso, Peterson Fluid Systems, JE Pistons, GZ Motorsports and Canton Racing products with regard to crank pressure control and proper oil control. What we found here may help prolong your engine life and possibly improve your chances of ending up in the winner’s circle. 

For illustration purposes, even the most mundane street car, can take advantage of Moroso’s Air/oil separator’s on unit.

 PCV and It’s Importance

All internal combustion engines generate some type of crankcase pressure in the form of blow-by. Blow-by is combustion gasses that escape past the piston rings. In the early 1960s, General Motors identified crankcase gasses as a source of hydrocarbon emissions. They developed the PCV valve in an effort to help curb these emissions. This was the first real emissions control device placed on a vehicle. While most of us who are performance enthusiasts will roll our eyes when emissions controls are even mentioned, GM actually did the performance world a favor here. 

These screenshots from Moroso's video show a factory PCV system in many cases is not up to the task. Side by side you can see the difference in the oil container at the beginning of the video (left) and at the end (right) after only a half-hour drive.

Not only does a properly operating PCV system reduce the overall emissions output of a vehicle while at the same time not sacrificing horsepower, it also has other benefits. It improves gasket seal, and prolongs gasket life by reducing the blow-by effect. Further, it also helps reduce the amount of oil an engine consumes through the combustion cycle, or loses due to leaking seals. 

Air-Oil Separators

Moroso Air/Oil Separator for race use. Unlike a street car system, this separator is a stand alone setup and not designed to return any gasses back to the engine.

Not long ago Moroso released a video of one of their air-oil separator systems in action. The separator was placed in-line with the PCV system on a stock Cadillac CTS-V. The car had only 24,000 miles on it, and the test drive lasted about thirty minutes. They included both hard acceleration, and just general cruising like the car would likely see in regular use. You can see several puffs of oil and water vapor enter the clear container that was substituted in place of the aluminum one for this video.

This is further evidence that the factory PCV system on a high-performance, unmodified engine, with low mileage is inadequate. The car’s owner states that after about a week of regular driving there’s typically about 3/4 of an inch of oil in the separator. While this may not sound like a lot, consider how much oil that is over the course of an oil change interval, a period of twelve to sixteen weeks on average.

So every twelve weeks the separator would accumulate about eight inches of oil in its reservoir. The actual volume would vary based on the dimensions of the separator, but that is definitely a substantial amount of engine oil. 

Removing this oil mist before it reenters the engine reduces detonation, and deposits on the intake track, including the valves themselves. – Thor Schroeder

Moroso’s Air-Oil Separators plumb directly into the car’s PCV system. Using mesh filter media, they capture the majority of the engine oil that escapes the crankcase and is normally sent back to the engine through the intake. “Removing this oil mist before it reenters the engine reduces detonation, and deposits on the intake track, including the valves themselves,” according to Moroso’s Thor Schroeder. 

Most of the separators have a total volume of just under a quart of oil and have a drain valve to allow the collected oil to be cleanly and easily drained into another container. Moroso offers these separators in both a universal style and direct fit for multiple vehicle specific applications. They also offer Air-Oil separators for dry sump and racing applications. These separators work much the same way that their street systems do, however they are designed for car’s running at the track rather than cars that are street driven on a regular basis. These systems do not plumb into the factory PCV system, instead they are stand alone separators. 

Moroso Air/Oil Separator for street use. These separators capture vapor and oil that has escaped into the PCV system. They trap the liquid and send the gasses back to the engine keeping the car’s emission system intact while improving engine performance.

Canton Racing Products also builds air-oil separators and chimed in on this subject. Jeff Behuniak of Canton tells us “An air-oil separator is important because it separates the blow-by from the oil in the engine.” Behuniak also pointed out that removing blow-by from the engine is critical to engine oil seal life, especially the crankshaft seals. 

Wet or Dry

It’s important to note that we’ll be discussing both wet and dry sump oiling applications. Within those discussions we’ll also be featuring various parts and components of those systems. Both of these systems are used in various high-performance scenarios ranging from street, to full-tilt race applications. For those unfamiliar with the differences or the specific advantages and disadvantages of each, we’ve included some additional information below.

Wet Sump Pumps

Most commonly we recommend an oil pump based on the clearances of the motor.

Wet sump pumps are what is found in the majority of street-duty engines. These pumps are driven off of the crankshaft or a distributor drive-shaft. A wet sump is just that. The oil pan is where all of the oil pickup occurs and where the oil resides in the engine. Oil is drawn from the pickup into the pump and pushed through the filter and into the oil galley passages within the engine casting. This is what lubricates vital engine bearings and components. Oil then returns via other passages to the pan where it resumes the cycle again.

In a wet sump, using the proper oil pump can make a considerable difference in engine output. It was long thought that running a high-volume oil pump was necessary in most high-performance applications. However, as Canton’s, Jeff Behuniak points out, this is not always the case. It all goes back to tolerances within the engine. “Most commonly we recommend an oil pump based on the clearances of the motor. With tight clearances you don’t need a high-volume pump because the void that the oil can fill is only so big. With a loose clearance motor you can use a high-volume oil pump because the amount of oil needed to fill the void is greater.” In a nutshell, matching the pump to a specific engine setup is another area where proper oil control could save you horsepower. 

Often, the biggest disadvantage to a wet sump system is the need to keep the pickup covered through oil control. This can become tricky in high-performance or spirited driving. Whether on the street, drag racing at the track, or turning through the corners on an autocross course, high-g loads can cause oil to move away from the pickup and leave the system open to cavitation.

Left: A Peterson Fluid Systems external wet sump oil pump. Right: A typical wet sump internal pump from Canton Racing Products.

This could potentially starve the engine of oil or at the least cause a drop in oil pressure. The solution is often to switch to a high capacity pan, some of which may even incorporate trap doors or baffles in an effort to trap as much oil around the sump as possible. On the other hand, there is a tradeoff in the form of less available space since those types of oil pans are typically much deeper. As such, a larger, higher capacity pan with more “tricks” to it will often take up more space, and potentially reduce ground clearance.

Dry Sump Systems

How Many Stages?

The number of stages in a dry sump system has a direct influence on several factors. The greater the number of stages, the more oil can be pulled back into the system and directed back into the engine where its needed. Typically, the greater number of stages also means more vacuum when those scavenge stages are not pulling oil, they will be pulling vacuum on the crankcase.

In a dry sump system, the oil still returns to the pan just like a traditional wet sump system. However, it’s immediately pulled away by the scavenge stage of the external oil pump. With no internal pump and no oil to hold, the pan itself is dramatically shallower. A dry sump pump is an external pump which can have one or multiple stages. The scavenge side of the pump pulls oil out of the pan and back to the tank or reservoir. The pressure side of the system then pumps oil into the engine. A typical setup will have one pressure stage and multiple scavenge stages. Other components to a dry sump system will include the drive system, oil tank or reservoir, air/oil separator, filter and oil lines.

A key advantage here is that a dry sump system can be used to direct oil as needed more effectively. Oil does not have to “wait” to make it’s way through the block and to various components. This can improve lubrication to all areas of the engine and also more effectively separates air from the engine oil.

Dry sumps can also more effectively collect and direct oil under all sorts of driving conditions. With a dry sump, the migration of oil in the pan under high-g loads is negated since the oil is collected almost as soon as it returns to the pan. This rapid collection also helps to ensure that the pickup is not starved for oil under such conditions that would cause the engine to suffer a drop in pressure or total lack of lubrication.

A tank or reservoir such as this is where the oil is stored in a dry sump system in lieu of it sitting in the pan.

Another key advantage to dry sump systems would be the shallow pan. By nature, these pans offer increased ground clearance, as well as the option to lower the engine in the chassis.

The collection of oil is also controlled more precisely in a dry sump system. Many systems will run three or more stages (see sidebar to the right). Regardless of the number of stages, there is typically only one pressure stage. The remaining stages are used to scavenge oil back to the reservoir or tank. Usually, the majority of scavenging will occur at the oil pan although some engine builders will also place a scavenge line at the engine valley to prevent oil from pooling there; directing it back through the system as quickly as possible.

The greater number of stages operating, the faster oil is pulled back into the system. This also affects the vacuum, as more stages increase the amount of vacuum being pulled when the system is not pulling oil. The biggest drawback to a dry sump system is often the cost and the available space required.

Moroso dry sump pumps. Left: Single stage. Center: Three stage. Right: Six stage.

Increasing Vacuum

This Peterson Fluid Systems external wet sump pump incorporates a section solely for vacuum as well.

Sometime in the late 1970s to early 1980s professional engine builders discovered that applying vacuum to the crankcase would in-fact improve engine performance. Wade Moon, from Peterson Fluid Systems, tells us, “Twelve to fourteen inches of vacuum is a pretty safe area to be at.” Vacuum applied at around twelve to fourteen inches of mercury (HG) will improve ring seal, allowing lower tension rings to be utilized.

This also improves oil scavenging, cavitation, and windage, getting oil away from moving parts and back to the pickup faster. Moon went on to tell us “We have had customers tell us they have seen a 35 hp increase pulling fourteen inches of vacuum.” This makes running a vacuum pump on a racing engine that much more appealing. 

Moon also pointed out two other key areas to keep in mind when selecting a vacuum pump. Block material is one; an aluminum block can be harder to pull vacuum in. At higher RPM the cylinder walls actually move a little, breaking ring seal which has an impact on overall vacuum. Fuel type is the other area to consider; gasoline or methanol. Methanol powered engines typically have greater blow-by, requiring a larger pump to generate and maintain proper vacuum. This is where it’s important to work with a vacuum pump supplier like Peterson Fluid Systems to select the proper pump setup.

Dry Sumps and Vacuum

With dry sump systems vacuum is applied to the crankcase whenever a scavenge stage is not drawing oil from the system. This means that there is not usually a need for a separate vacuum pump in a dry sump system.  “All dry sump pump scavenge stages will move oil and air. Not all scavenge stages are pumping oil all the time, so if there is no oil then they move air,” says Moon. How much vacuum is determined by the pulley selection, design of the pump, number of stages, and the amount of time each stage spends scavenging oil compared to the time it spends creating vacuum. This means that in a dry sump setup, vacuum must be monitored appropriately to ensure that it’s being applied properly throughout the engine’s operating range.

Wet Sumps and Vacuum

With a wet sump system, a separate vacuum pump is necessary or may need to be incorporated into the oil pump should an external pump be utilized. A separate vacuum pump could be added on as an engine accessory, driven off the belt. This vacuum pump would draw crankcase pressure, typically from the oil pan and it’s speed would then dictate the amount of vacuum pulled. The speed would be regulated via the pump’s driven pulley.

Left: Moroso vacuum pump, typical for a wet sump application. Right: You can see how the vacuum pump mounts much like any other engine accessory to be driven by the crankshaft.

General Precautions When Running Vacuum

The proper regulation of vacuum is another area to consider. Some systems will utilize a regulator to control the vacuum. In other cases, engines will have an added vent at the back of the valley providing a controlled bleed off. This vent should be filtered and be of proper size to regulate the engine vacuum. This is essentially a bleed that allows outside air to be introduced, reducing the vacuum affect that the pump has.

In road racing applications, and some drag racing instances where there is frequent throttle fluctuation from changing conditions or “pedaling” the throttle, there may also be a need for a pop-off valve to help relieve built up pressure. Under these circumstances, the engine can actually go from a vacuum situation to a positive pressure situation. Generally, these pop-off valves have one-way operation and are typically placed on the valve cover. They open at a specified pressure and allow crankcase pressure to vent to the atmosphere. 

The use of a vacuum regulator, vent, or pop-off valve is often necessary when running crankcase vacuum.

Our Project Blown Z uses a dry sump system for oiling and vacuum.

Wet Sump Precautions

If you choose to run vacuum in a wet sump system there are other areas to take note. The oil pump type, pan volume, and pickup location are even more critical under these circumstances. Since you are applying vacuum to the crankcase itself, you would actually be working against the oil pump. In essence, both pumps are applying a type of suction to the same area of the engine. The vacuum pump is trying to draw air, and the oil pump is trying to draw engine oil. Inevitably, this will cause the oil pump to work harder, operate at lower pressure or even cavitate, which could be detrimental to the longevity of your engine.

The Vacuum Pump Effect With GZ Motorsports

Any properly-built engine can benefit from the addition of a vacuum pump, but the results will vary depending on the amount of blow-by it generates and any air leaks that may be present. For the maximum benefit to be realized, a looser piston ring package is optimum; however, the use of a vacuum pump doesn’t have to be factored into the initial build.

One way to decrease blow-by and increase piston ring seal is to add an aftermarket vacuum pump. Vacuum pumps work by creating negative airflow (vacuum) thereby pulling the air from the crankcase. They are rated by their airflow capacity measured in cubic-feet per minute (CFM) and are available in a variety of sizes. Which pump is right for you depends on your engine combination and variables.

A smaller, naturally aspirated engine will effectively utilize a smaller pump than a larger displacement engine or one that employs power adders such as nitrous, superchargers, or turbo systems. These engines produce higher crankcase pressures and, as such, necessitate a larger pump or greater RPM from a smaller model. A properly sized vacuum pump can net positive results in just about any engine. Your powerplant will enjoy increased ring seal, improved combustion, and less contamination of the intake charge. All of these benefits can improve your engines power output.

If you’re in the planning stages of your engine build, a vacuum pump allows for the use of looser, or low-tension, piston rings. This type of ring produces less friction on the cylinder walls and, as with any part of your performance machine, less friction equals more power. However, it’s important to note when using a standard tension ring package, typically, the horsepower increase won’t be as drastic. Horsepower is usually lower from the pump because of the increased leakage as compared to the low tension ring package.

We placed a 454ci big-block LSx on the dyno, then installed a GZ Motorsports Sportsman pump for additional power. You can read up on our latest GZ Motorsports vacuum pump testing, here.

Ring Seal and Pistons

Ring seal plays a vital part in how your engine uses oil and performs as well. Proper ring seal reduces blow-by, thus decreasing pressure inside the crankcase. Running a vacuum pump in a racing engine, you can actually change to a lower tension ring package, using back cut rings instead of the older style high-tension D-rings. This allows for lower internal friction and an improvement in overall engine performance. 

We talked with Gary Meier of JE Pistons about this. Meier tells us “Ideally you want a back cut ring with gas port pistons, the system seals better and is more efficient. If you run with a D-wall ring you are only going to gain a minimum amount of power.”

Meier points out that using gas ported pistons with lateral ports is the best choice. “In the old days, guys would argue that the gas ports would get clogged up and then they weren’t doing any good. These days the fuel is so much better that it has eliminated that argument unless you are running extremely rich or something else is wrong,” says Meier.

Since running a vacuum pump pulls oil away from rotating components and back to the pan, windage is reduced. The more is better approach does not apply to engine vacuum however. Running a high level of vacuum can have an adverse effect on engine life.

While Meier was able to tell us “On a standard 600 hp engine, 22-23 hp is not out of the question with vacuum at around 14-15 inches of mercury.” While some high-end race cars will push beyond those numbers to run over twenty inches of vacuum, these are cars that are generally towed and pushed through the staging lanes and their engines live the majority of their lives either warming up for a race or making a pass at the track. 

“Above 14-15 inches of vacuum, you pull too much oil away from the wristpins and cylinder walls,” said Meier. In these cases, the higher end engines will employ measures such as oil squirters to spray the wrist pins, as well as special camshaft squirters, and even other provisions to oil the rocker arms and valvetrain. All of this must be taken into account when running higher levels of vacuum. 

While vacuum pumps in the past have been thought of as something for high-end dry sump race engines only, they can also increase the power in a wet sump system as well. Meier recommended this for drag race engines only however. He also stated that the horsepower gains would not be nearly as significant as it would be with a dry sump system. In wet sump systems the expected horsepower gains would be in the neighborhood of 6-12 horsepower.

The same rules apply with regard to running too much vacuum. Peterson Fluid System’s, Wade Moon, pointed out that his company offers a single-stage wet sump external pump with a section on it just for pulling vacuum. 

Oil Pans  and Accumulators

Obviously we need to touch on these subjects as well when discussing engine oiling and control. We got with Canton’s, Jeff Behuniak, on this subject to discuss the importance of having the proper oil pan and the role other parts can play in many engine applications.


Having the proper pan is critical for oil control. If the oil pickup is located in the oil pan then the pickup needs to remain covered under all driving conditions. Whether a car is cruising down the road, making a quarter-mile pass at the drag strip, or turning corners on an autocross or road course. Behuniak tells us “In a well designed pan the oil will keep the pickup covered and keep your engine pressure where it needs to be.”


Products such as Canton’s Accusump  allow the engine to be “charged’ with oil on cold start, by releasing pressurized oil into the engine prior to ever cranking it. This system can also provide oil to the engine if the oil pressure should drop, allowing for engine oil to continue flowing for several seconds from the Accusump’s reserve, and possibly staving off catastrophic failure.

What’s This All Mean

Setting up an engine’s oiling system with the proper parts and understanding can give you a gain in horsepower, reliability, and a major advantage out on the track. Proper attention to detail must be paid and each component must be matched correctly.

In racing, the difference between the winners and the losers is sometimes only a few thousandths of a second, which in the end could boil down to a couple of horsepower that you saved by paying attention to the small details that may make a big impact. Even running an oil/air separator on your street driven car, especially in boosted applications has multiple advantages and may prolong engine life and reduce the need for repairs in the future. Just like with everything else; research, research, research and you’ll be well on your way to some winning passes.

About the author

Don Creason

Don Creason is an automotive journalist with passions that lie from everything classic, all the way to modern muscle. Experienced tech writer, and all around car aficionado, Don's love for both cars and writing makes him the perfect addition to the Power Automedia team of experts.
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