Oil pressure is something every engine builder worries about. Low oil pressure or a loss of pressure can cause expensive warranty problems and catastrophic engine failures, neither of which is good for your business.
Though the “bigger is better” mentality persists, most engines only need about 10 psi of oil pressure for every 1,000 rpm of engine speed. Some performance engine builders are running even less to reduce the horsepower it takes to drive the oil pump.
Idle oil pressure is especially important because low oil pressure at idle can cause valvetrain noise by starving the camshaft, lifters or followers and rocker arms for oil. Overhead cam engines are more susceptible to low oil pressure at idle than pushrod engines because of the long distance oil must travel to reach the upper cylinder head area.
When the engine is idling, the oil pump is rotating very slowly (typically at half crankshaft speed). There’s not much oil volume moving through the pump, so if there is too much clearance inside the pump, or there is leakage where the pump mounts to the engine block, the engine may not develop normal oil pressure. Likewise, if the engine was built with looser clearances in the main and rod bearings, the pump may not be generating enough flow to develop normal oil pressure.
A high volume oil pump with taller gears that displaces more internal volume is one way to assure adequate oil pressure at idle and as engine rpm increases, especially in engines with increased bearing clearances. Heavier viscosity oil is another option that can help maintain oil film strength for higher oil pressure readings, especially when the oil gets hot and thins out in engines with extra bearing clearance. But there are tradeoffs with using a heavier viscosity oil such as 20W-50 racing oil. Heavier oils create resistance to flow, which means the oil pump has to work harder to pump the oil. More drag equals more parasitic horsepower loss.
In late model engines such as the Chevy LS series, Ford 4.6L modular V8 and the new Chrysler Hemi, the oil pump is not mounted on the bottom of the engine, but is located above the crankshaft in the front of the engine. This was done mainly for packaging reasons. But it creates some potential problems for several reasons.
The front location means the oil pump sits high and dry. The vertical position of the pump means oil drains out of it when the engine is shut off. What’s more, oil has to travel a much further distance to reach the pump before it can start to generate any pressure in the engine. Consequently, the pump has to have relatively tight tolerances to pull the oil up from the crankshaft. It also helps to use a thinner viscosity oil that flows easily when cold such as a 5W-30, 5W-20 or even a 0W-20. That, in turn, requires relatively tight bearing clearances to maintain proper oil pressure within the engine.
Another issue with front mounted oil pumps is that some of these pumps tend to leak quite a bit of oil as pressure builds at higher rpms. The Chevy LS engines have a stamped steel cover on the oil pump, while Ford uses a aluminum cover and Chrysler uses a cast iron cover. The cast iron cover is the most rigid of the three and flexes the least under pressure. But the relatively flimsy aluminum cover that Ford uses has little rigidity and spews oil out the sides like a fire hydrant at high rpm. That’s not good for maintaining oil pressure at higher rpms.
Mike Osterhaus of Melling Oil Pumps, Jackson, MI, said his company uses a strong cast iron cover for their front-mounted Ford and GM replacement pumps. The cover is not available separately but comes with the pump. “The increased rigidity of the cover stops the flexing and leakage that occurs with the stock covers,” he says.
“We feel our high volume Chevy LS oil pump performs better than a ‘blueprinted’ or modified stock pump, which is a good choice for performance engines built with loose bearing clearances. We also make internal improvements in our pumps so they outperform the OEM pump,” Osterhaus says.
“Why modify a stock pump if you can buy a new performance pump that has better flow characteristics right out of the box? All of our pumps are built to close tolerances so they will maintain good hot idle oil pressure, meaning there’s really nothing to be gained by modifying or select fitting internal pump components,” Osterhaus says.
“Another problem we see is oil pump galling in modified Ford modular V8 and V10 engines,” he continues. “The OEM pumps have very tight tolerances, so they can be adversely affected by crank movement if the engine has been modified to produce more power. Our replacement pump for these applications uses a billet steel rotor, and a hard anodized coating on the housing to improve durability. The inlet is also CNC ported to optimize flow.”
A front mounted oil pump can also create misalignment problems if the engine block is line bored to restore worn main bearing bores. Changing the center line of the main bores changes the relative distance between the centerline of the crankshaft and pump. If corrective measures are not made to maintain the same distance as before, it will jam up the pump.
Another problem that can disrupt oil delivery and cause internal pump wear is cavitation. All oil pumps may experience cavitation at some speed, but gear type pumps are more susceptible to this problem then gerotor pumps. When the gear teeth pass over the pump inlet port, oil is pulled up into the area between the teeth. As the speed of the pump increases, there is less and less time to fill the cavity between each tooth.
Eventually the point is reached where the suction created by the spinning gears causes the oil to vaporize and form tiny bubbles in the wake of each tooth. This causes a loss of flow and pressure because the pump is now churning vapor rather than pumping liquid. What’s more, when the bubbles implode, the shock waves erode the metal surfaces inside the pump. Over time, this can increase pump clearances and cause a permanent loss in oil pressure.
In a stock Chevy small block oil pump, cavitation typically occurs around 5,500 rpm, causing the pump’s output to flatline regardless of how much faster the engine revs. This can cause a potentially dangerous drop in oil pressure just when the engine is needing more oil, not less.
Different manufacturers have developed different solutions to the problem of cavitation. Bob Sanders of Titan Speed Engineering, Ojai, CA, says his company only makes gerotor- style pumps, primarily for Top Fuel drag racers, but also for oval track racers, too.
“Stock oil pumps are made for engines that spend most of their time at speeds below 3,000 rpm. They all have problems with cavitation at high rpm. Our gerotor pumps are dual feed pumps that fill from both ends, so there is much less risk of cavitation. Our newest pressure pumps have what we call Progressive Pulse Technology (patent pending) that uses a unique shape in the suction and discharge kidneys inside the housing.”
Sanders said Titan’s Professional-series wet sump oil pumps are made of high strength 7055 T-7 billet aluminum with a hard anodized coating. The pumps are bolt-on replacements for popular Ford, Chevy and Chrysler V8s, though the baffles inside some aftermarket oil pans may have to be modified to accommodate the larger pump.
The main pump shaft features a tool steel hex drive and rides in needle bearings for added durability. It’s a less complicated pump than a dry sump oiling system, though Sanders said he is also developing a new dry sump system that will move approximately 40 percent more oil than earlier dry sump systems.
Titan also makes less expensive Sportsman-series oil pumps for Chevy and Ford V8s which are also billet aluminum, but use a T-6 heat- treated 356 aircraft alloy.
Jon Kaase of Jon Kaase Racing Engines, Winder, GA, is also a believer in the gerotor-style oil pump. “We make a gerotor pump for big block Ford V8s that feeds oil into both sides of the pump. It’s a cast iron pump, but much stronger than the stock Ford pump which sometimes cracks and falls off into the oil pan! Our pump does not break like the stock pump, or suffer cavitation problems like gear set style pumps.”
Osterhaus of Melling says cavitation is a function of the inlet design of an oil pump. The vapor pressure of the oil versus the pressure drop that occurs from the oil pan pickup to the pump is what creates the conditions that lead to cavitation. If the pressure drop is greater than about 4 psi, vapor bubbles will form inside the pump. The bubbles will collapse on the high pressure output side of the pump. But when they do, the force generated by the implosion of the bubbles can erode the metal surfaces in the pump.
The point at which cavitation starts to occur depends on pump speed and the size of the pickup tube, says Osterhaus. “Up until the early 1990s, GM used a 5/8? OD pickup tube on its V8 engines. In 1993, GM changed to a larger 3/4? tube that flowed better and produced less cavitation. We still make the M55 oil pump for the older applications, but recommend the newer M155 pump with the larger inlet as a retrofit for better oil flow.
Osterhaus says Melling has also improved the inlet design of its pumps to improve flow and reduce cavitation up to 8,000 rpm. This allows the pump’s output to continue to climb without flatlining above 5,000 rpm like a stock pump.
“You don’t really need a high volume pump if you are running stock bearing clearances. This will save power compared to a high volume pump. But if you are running a lot of rpms or are building an engine with looser clearances, then a high volume pump would be the best choice.”
Melling also makes billet pumps for performance applications, which Osterhaus says are an affordable alternative to dry sump systems, and are recommended for engines that rev above 5,000 rpm. A unique feature of these pumps is that the gear shaft extends through the gear into the pump cover to reduce deflections that can rob power from the engine.
Moroso of Gilford, CT, a company well-known for its performance oil pans, says many stock and so-called “race” pumps are not equipped to handle higher oil flow at race speeds. As oil velocity increases, many pumps cavitate and chatter because they just can’t handle the extra demand.
Moroso Racing Pumps are specifically engineered to accommodate the oil flow required by consistently higher engine speeds. Special anti-cavitation slots, feeder grooves and an enlarged bypass area are machined into the housing to bleed oil back to the inlet side of the pump. These features combine to offer a smooth and consistent flow of oil, which improves the pump’s overall performance, extends engine life, and places an even loading on the distributor shaft to eliminate spark scatter.
“Assuming you are looking at an internal wet sump pump, you would look for these characteristics in a modern oil pump,” explain’s Moroso’s Kevin Brown: “Enough pump displacement to yield adequate oil pressure at a hot idle and all the way through the useable rpm range. You want to see a nice clean linear pressure trace until the regulation point of the pressure relief valve. At the point of pressure regulation it should maintain near constant pressure level. And, you should look for a heavy duty casting to withstand the rigors of the racing environment.”
Moroso Racing Pumps include Professional Billet Aluminum Gerotor pump, Sportsman Billet Aluminum Spur Gear Pump, and the cast iron Blueprinted Racing Oil Pump that is CNC machined to ensure the tightest tolerances. The Blueprinted pump has anti-cavitation slots and enlarged feeder grooves to provide a steady flow of oil to each side of the gears for high rpm lubrication, cavitation relief and reduced spark scatter.
Moroso also makes an External Wet Sump Oil Pump that mounts outside the engine (similar to a dry sump setup). This allows the use of a full-length windage tray inside the oil pan for less windage and more power. Moroso says their External Oil Pump also eliminates torsional stress on the camshaft, as well as spark scatter and resultant horsepower loss caused by an internal wet sump pump.
Brown, a Moroso sales engineer, says a properly designed inlet circuit is key to limiting cavitation. “You need to have the correct diameter inlet with minimal lifts and bends to mitigate piping losses and oil velocity limitations, as well as a properly designed inlet strainer (pick up) to minimize pressure loss at the inlet,” says Brown. “Then, you must set the correct pick-up height off the floor of the oil pan to minimize vortexing at the pick up. A well-designed windage tray will help protect the oil from aeration, and of course you must be sure there is suitable oil volume in the oiling system to eliminate any drainback and oil turnover issues.”
Vern Schumann of Schumann Sales & Service, Blue Grass IA, feels a solution for cavitation in the Chevy SB/BB oil pump is his dual feed design that flows 60 percent of the oil into the pump housing through the main inlet, and 40 percent into the housing through a second inlet. There are also cavitation relief channels cut into the pump cover (which are machined with a unique water jet process).
There is also a risk of starving the engine for oil at higher speeds with heavier viscosity oils. The screens or perforated metal covers on most oil pump pickup tubes are fairly restrictive. And the heavier the oil, the less easily it flows through the pores in the screen or perforations.
Wet sump oil pumps don’t generate a lot of suction, so any restrictions on the inlet side of the pump can starve the pump and reduce oil pressure. Long pickup tubes with restrictive inlets, therefore, are bad news if you are trying to maintain good oil pressure in a performance engine or even a stock engine.
Schumann says he has researched this issue extensively after discovering his new dual feed high volume small block Chevy oil pump was not realizing its maximum flow potential with commonly available aftermarket pickups.
“Our pump is fully capable of delivering up to 12 gallons of oil flow per minute. But it can’t achieve those flow numbers with any of the aftermarket pickup tubes I’ve tested. The pickups are too restrictive because of the size of the screens or perforations they use.”
Schumann said he has flow tested a variety of aftermarket pickups and found that all are overly restrictive and inhibit oil flow, especially with higher viscosity motor oils. For every 10 point increase in the viscosity of the oil, our tests show about a 5 percent drop in oil flow through the pickup screen.
An OEM style oil pickup with a screen style inlet cover has a theoretical open area of 60 to 70 percent between the wire mesh. Yet it only flows about 30 percent of what it should flow due to the restrictive drag created by the screen. Aftermarket pickups with perforated metal inlets are no better. In some cases, says Schumann, their flow characteristics are even worse!
The size, shape and spacing of the inlet holes in the aftermarket pickups vary from 29 percent to 49 percent (which is actually a lot less than the typical OEM screen style pickup) according to Schumann’s analysis. The flow rates range from a low of 20 percent in the poorest design up to a maximum of 37 percent in the best design which is far less than what you would expect from an aftermarket “performance” pickup.
Schumann says the industry needs to rethink the validity of current pickup designs because existing designs create a bottleneck that restricts oil flow to the engine regardless of what brand or style of oil pump is used. “The screen or perforated holes at the pickup inlet don’t really protect the oil pump. They just keep big chunks of debris out of the pump. The tolerances inside an oil pump are typically .002? to .005?, so any particles larger than that but smaller than the openings in the pickup inlet will be sucked into the pump anyway and damage the pump.”
Schumann said he worked with a dozen different automotive, aircraft and industrial filter manufacturers to develop a cartridge filter or other filter that could be installed in the oil pump inlet or pickup inlet to protect the pump. But they all concluded it couldn’t be done. Any such filter would be too restrictive due to the low suction qualities of wet sump oil pumps.
So Schumann came up with a different approach. Since the pickup screen or perforations don’t really do much to protect the oil pump anyway, and only create a restriction, why not open up the pickup inlet to improve its flow characteristics? Schumann’s solution is to replace the existing screen or perforated metal inlet cover with a 1/4? hex honeycomb cover that has an open area of 92 percent and flows up to 78 percent of its theoretical maximum. There is still some protection to prevent large chunks of debris from entering the pickup, yet much less restriction to impede the flow of oil at higher engine rpms.
Schumann said he is working with several aftermarket pickup manufacturers to produce the new low restriction pickups, and hopes the entire industry rethinks their current designs and adopt his new approach.
“Another modification that can improve flow to the oil pump is to cut the inlet end of the pickup tube at an oblique angle rather than a straight cut. This increases the effective area of the opening and allows better flow into the pickup tube.”
Schumann also cautioned that pickups with welded perforated metal covers may contain weld splatter inside that can flake loose and enter the oil pump. “If you pound the pickup against a pine board several times, you’ll often shake loose several weld BBs that are hidden inside the pickup. At least one pickup manufacturer I know has revised its welding procedure to reduce the risk of weld splatter ending up inside the pickup. But others have not, so you need to check the pickup tubes to make sure there’s nothing lurking inside that could cause problems later on.”
One often overlooked area where oil pressure and flow can sometimes be lost in a rebuilt engine (or even a new engine, for that matter) is the area where a bottom mounted oil pump mates to the block. The OEM mounting is simply a flush surface with no gasket or O-ring on most engines. Consequently, if both surfaces are not perfectly flat, gaps may allow high pressure oil to leak back into the crankcase. This can cause a drop in oil pressure at idle.
Schumann’s fix for this is a thin copper gasket that fits between the pump housing and block. The gaskets are currently available for small block and big block Chevy, and Windsor Ford V8s.
Rebuilt Oil Pumps
Osterhaus said hot idle oil pressure is critical in any engine, whether it is stock or performance. An engine builder can resurface the cover on a worn pump to restore end clearances, but it won’t restore the clearances between the gears or the gears and the sides of the oil pump housing. Because of this, a worn pump won’t deliver the same pressure as a new pump.
“We’ve supplied oil pump rebuilding kits to the aftermarket, but the better approach is to go with a new pump because the housing is often worn,” Osterhaus says.
If you’re worried about maintaining the oil pressure in your newly built engine, that’s a good thing. Not being sure of the oil flow demands will be a real problem for your customers.