Oil is the lifeblood of every engine. Any significant loss of oil pressure can destroy an engine in a split second so the oiling system must provide a constant supply of oil under all operating conditions.
With performance engines, keeping the engine lubed with a steady supply of oil can be a challenge because of the G-forces that may be encountered. One of the most demanding applications is the marine environment. Strapping a big V8 or a pair of V8s into a boat hull and running at full throttle across water can push any oiling system to the limit. The constant pounding and bouncing of the hull against the waves makes it hard to keep a wet sump pickup fully submerged in oil all the time. That’s why a dry sump system is often the best way to go for a marine performance engine.
The challenges are similar in road racing. The high lateral G-forces (up to 2 G’s) combined with hard braking (up to 3 G’s) and rapid acceleration (up to 1.5 G’s) create a lot of sloshing inside the oil pan. Baffles and trap doors in the oil pan can control oil movement to some extent, but a dry sump setup is usually better for this type of racing. A shallow dry sump oil pan also allows the engine to be positioned lower in the chassis to keep the center of gravity closer to the ground.
With off-road racing, vertical G-forces can pull the oil away from the bottom of the oil pan in a wet sump system. Every time the vehicle leaps over a hill or flies through the air, the oil pump pickup may suck in air, causing a momentary drop in oil pressure. Again, a dry sump setup can provide a more reliable supply of oil under such demanding conditions.
With circle track racing, the car is always turning left so the oil wants to climb up the right side of the oil pan. Extending the oil pan sideways on the right side and using baffles, trap doors and an offset pickup helps keep the pickup submerged in oil so the pump can deliver a steady supply of oil. A dry sump system can do the same thing while offering some ground clearance advantages with a shallower oil pan, but the typical Saturday night dirt track racer usually can’t afford a dry sump system. Track rules may also prohibit the use of a dry sump oiling system, depending on the class.
As for drag racing, it’s all straight line acceleration down the strip. The oil wants to climb up the back of the pan, so a deep oil pan with baffles and extra oil capacity is usually recommended to maintain steady oil pressure for the duration of the run. Don’t forget there’s also deceleration at the top end once the vehicle passes through the timing lights, so baffles or a trap door inside the pan that prevents the oil from sloshing forward is also a good idea.
Street performance is probably the easiest oiling application to deal with because the G-forces acting on the oil in the crankcase are less severe and less abrupt. Most street performance cars and trucks are driven the same as a stock vehicle 95% of the time, so a stock wet sump oil pump and stock oil pan are usually adequate. Extra oil capacity is always nice because it helps keep the oil cooler and adds some extra insurance against oil starvation under hard use.
For higher horsepower engines or street/strip applications, an aftermarket performance oil pan with baffles and extra capacity would be recommended. A high volume oil pump might also provide some additional cooling for the bearings and be better able to maintain oil pressure at higher engine speeds.
Oil Pump Tech
With most wet sump oiling systems there are two basic designs: a twin-gear or gerotor-style oil pump mounted inside the oil pan on the underside of the engine block, or a crankshaft-driven gerotor pump mounted on the front of the engine (Chevy LS, Ford modular, etc.). A stock oil pump is usually adequate for stock or slightly modified engines. But if you are building a high-power, high-revving engine with extra bearing clearance, a high-volume oil pump usually becomes necessary.
There are several factors that affect the flow characteristics of wet sump oil pumps. The pump’s flow capacity depends on engine rpm and the displacement of the pump. The faster the pump turns, the more oil it flows – up to a point. Above a certain rpm (typically around 5,500 rpm for SB/BB Chevy oil pumps), flow tends to level off because oil flow into the pump can’t keep up. The flow capacity of the pickup screen and pickup tube become a restriction that limits how much oil the pump can deliver to the engine.
Cavitation occurs when bubbles form inside the oil pump. When the oil that is being sucked into and pushed out of the pump can’t keep up with the gears, tiny vacuum bubbles form on the trailing edges of the gears. These are similar to the bubbles that form behind a high-speed boat propeller. The bubbles create drag, reduce pumping efficiency and cause a drop in oil pressure. Over time, they can also erode the surface of the gears. Cavitation can also occur when air is sucked into the pump. Aerated oil causes a similar drop in pumping efficiency, oil pressure and flow. Either way, cavitation is bad news.
The thicker the viscosity of the oil, the harder is it to pull it up the pickup tube into the pump. Using a lower viscosity synthetic oil can help here because it flows easier and is less likely to cause cavitation inside the oil pump at higher engine speeds. The most important factor, however, is the diameter of the pickup tube and the type of inlet screen on the pickup in the oil pan. Small pickup tubes and/or a restrictive inlet screen can be a major cause of oil pump cavitation.
The inlet screens or drilled covers that are found on some aftermarket performance oil pump pickups can actually restrict oil flow at higher engine speeds – especially when they are used with a high-volume oil pump. The larger the mesh size of the pickup screen or the diameter of the drilled holes on the pickup cover, the better. The only function the screen or cover performs is to prevent big chunks of debris from being sucked into the oil pump. The pickup provides no meaningful filtration because the clearances inside the oil pump are usually only a few thousandths of an inch so any debris larger than that will cause interference or damage inside the pump.
With wet sump performance applications, use the largest diameter pickup tube that will fit the pump. Many aftermarket performance oil pumps have larger inlets for this very reason. According to one source, if the diameter of the pickup tube is 20- 30% larger than the inlet port on the pump, the tube will never become a restriction or cause cavitation inside the pump.
Also important is making sure the oil pump pickup tube and inlet are correctly matched to the oil pan, and that the inlet is positioned at the correct height above the bottom of the pan (typically 1/4? to 3/8?). If the inlet is too close to the pan, the narrow gap can restrict flow. If the inlet is too high in the pan, the pickup may suck air under hard cornering, accelerating or braking. Oil problems caused by mismatched oil pans/pickups and mislocated pickups are more common than you think.
Oil flow can be increased by carefully porting, blending and rounding any sharp edges in the oil pump inlet and outlet ports, by minimizing clearances between the pump gears and the gears, housing and cover (typically .0015? to .002?), and by using a pump with taller or larger gears. A high-volume pump is often necessary for a high-revving engine or one with looser bearing clearances.
The pressure delivered by the pump depends on the spring in the oil bypass valve. The stiffer the spring, the higher the relief pressure of the bypass valve and the more oil pressure the pump delivers before the bypass valve opens.
The old rule of thumb of running 10 psi of oil pressure for every 1,000 rpm is still valid for most applications. But some racers are getting by with less oil pressure and are gaining anywhere from 5 to 30 or more horsepower! It takes a certain amount of horsepower to drive an oil pump, so using the least amount of oil pressure that’s necessary to maintain a safe level of lubrication saves power that would otherwise be needed for the pump. Many NASCAR teams are running less than 5 psi of oil pressure per 1,000 rpm, and are using low viscosity synthetic oils with tighter bearing clearances to keep the oil film in the bearings.
Most oil pumps use an internal bypass valve to vent excess oil pressure. The advantage with this design is that it delivers oil at a steady pressure while allowing pressure to build quickly in a cold engine. The drawback with this setup is that during deceleration, oil can actually flow backward from the pump into the pickup tube.
When the driver stabs the throttle to accelerate, there can be a slight delay in oil delivery until the reverse flow is overcome and oil is again flowing in the right direction into the pump. By comparison, some racing pumps have an external bypass valve that dumps excess oil pressure back into the crankcase. This prevents the reverse flow effect and helps maintain a steady flow of oil when an engine is decelerating and accelerating rapidly.
Some performance oil pumps also use a ball bypass valve rather than a piston or cup-style bypass valve. Ball valves are used in automatic transmissions because they are self-cleaning and less likely to stick.
“Energy Recovery” Oil Pump
Every oil pump needs a bypass valve to vent excessive pressure, otherwise bad things might happen to the pump or engine if oil pressure was not controlled. But every time excess oil pressure is vented through a bypass valve it represents lost energy. Verne Schumann of Schumann Sales & Service has come up with a way to recover much of this lost energy with his newly patented “Energy Recovery” oil pumps for SB/BB Chevys and Fords.
Schumann said the new “ER” design “diminishes the input effort required, yielding the same gallons per minute (gpm) volume and pressure as high-effort pumps. Normal internal hydraulic pump by-pass lock-ups are eliminated. Unique energy recovery engineering converts spent energy into active input oil supply flow.” Schumann said his new ER pumps are 30% more efficient and significantly reduce the power needed to drive the pump.
Schumann is not making any specific horsepower claims for his pumps, but on one dyno test, an engine showed a 10 to 15 hp improvement by simply changing the oil pump.
Schumann’s Energy Recovery pump uses an external hose to connect the bypass valve discharge port to the pickup tube. By rerouting oil back into the pickup tube, the oil pressure that would otherwise have been wasted is reused to feed the pump. It has a siphoning effect that improves oil flow into the pump and reduces the chance of oil starvation when the engine is accelerating hard or is experiencing lateral G-forces.
Chevy LS Oil Pump Issues
The front mounted oil pumps on Chevy LS engines have been a challenge for many engine builders. The pumps on these engines have critical clearances that require the pump gears to be precisely centered with respect to each other and the pump housing. The recommended procedure is to mount the oil pump with the block out of the vehicle sitting upright with the crankshaft in a vertical position so the crank will be centered in the main bearings.
Shims must then be positioned between the inner and outer gears, and the outer gear and housing before the four housing bolts are tightened down to secure the pump to the block. If this procedure is not followed, the oil pump may bind and/or break as soon as the engine is cranked or started.
The stock pump housing can also be easily distorted if it is clamped in a vice, causing the pump to bind when it is installed on the engine. Schumann makes a special work fixture that allows the LS pump to be held securely without bending the housing.
Mike Osterhaus, Product Development Manger for Melling said the front mounted oil pumps on many late model engines has created opportunities for engine builders because many original oil pumps cannot meet the demands of a performance engine.
He said Melling’s line of “Select Performance” oil pumps eliminates those issues while supplying increased performance and durability at an affordable price. Osterhaus said that aftermarket oil pumps for the Chevy LS engine and similar applications are available from a variety of sources, but that many of those offerings are based off original equipment oil pumps.
“The original equipment pumps cannot compete against the performance and durability of a Melling performance oil pump, which was designed from the start to be used in performance engine applications.” He said improvements include increasing the pressure tightness of the pump assembly to reduce oil leakage.
Crank-driven pumps have larger surface areas which need to be sealed. Reducing the leakage coming from the pump results in improved oil quality and flow delivered to the main gallery. The pumps are also cast in 356-T6 aluminum, precision CNC machined and hard-coat anodized for improved durability.
Galling can also be a problem in some applications, such as GM 5.3L, 6.0L and 6.2L V8s. A severe galling condition can arise from the tolerances and materials used in the original GM oil pumps. This situation cannot occur in the Melling oil pumps because of changes that have been made in the design of the pump itself. “Our high-volume 10296 performance pump for the Chevy LS flows 18% over stock, and delivers improvements in flow and pressure across the entire engine operating range, not just at hot idle.”
Another option for the LS is to eliminate the stock front mounted gerotor pump altogether and use an external oil pump. TJ Grimes of Baker Engineering/Pro Cam said his company makes a Chevy LS wet sump oil pan conversion that retains a wet sump setup but uses an external pump like that from a dry sump system to supply oil to the engine.
The oil pan is only 6-1/2? deep but is 13? wide and holds 7 quarts of oil. The modification requires blocking the oil ports for the original front-mounted pump. The conversion eliminates the long pickup tube that can delay flow to the stock pump and reduces the risk of oil starvation.
Grimes says the trend is to make wet sump oiling systems work like a dry sump system but without the cost or complexity of a full dry sump system. “You can keep windage down inside the crankcase by using scrapers to pull oil away from the crank.”
Dry Sump Systems
With dry sump oiling systems, the setup is entirely different than a wet sump system. Most dry sump systems use one to four or more scavenge pumps to suck oil out of the pan (and other locations on the engine), and one or two pressure pumps to feed oil back into the engine. Oil aeration is controlled by using an oil/air separator and routing the oil into a vertical storage tank before it is pumped back into the engine.
The tank adds additional oil-holding capacity to the system to help keep oil temperatures down. The external plumbing makes it easy to add an external oil cooler as well. Pulling oil and air out of the crankcase also increases horsepower by reducing windage and drag on the crankshaft. The only drawback with dry sump systems is their cost, which can range from $1,500 up to $3,500 or more, depending on the setup.
Bill Dailey of Dailey Engineering says his company specializes in high-end custom dry sump pumps and pans for racing applications. “A lot of people sell off-the- shelf components for dry sump oil systems. We do too. But many racers want special mountings or designs to fit their specific race car. So most of what we do is custom work for racers.”
One such product is a custom billet oil pan with an integral oil pump. “They won’t allow it in NASCAR, but where rules allow it, the setup provides a smaller and cleaner installation,” said Dailey.
What kind of oiling system you ultimately decide to use in an engine you are building will depend on the application, your customer’s wishes and how much money he is willing to spend to keep his engine lubed. Lubrication is one area where you don’t want to take chances.