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Oil Pump Technology

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.

By Larry Carley

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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.

Front-Mounted Pumps

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.

Pump Cavitation

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.