Moroso dry sump oiling systems incorporate a shallow oil pan with multiple pickup points, remote dry sump storage tank with integral breather, multi-stage pump, and drive mandrel with cog belt.
Lubrication is the critical lifeblood of every racing engine. Without it, the engine’s lifespan is measured in seconds. The oiling system is designed to deliver a constant supply of clean, filtered oil to properly lubricate all of the engine’s moving parts. This includes the engine bearings, pistons and piston pins, camshaft and valve gear, and all the associated parts that make the engine run. In concert with its lubricating function the oiling system may also be utilized to cool certain parts such as the valves springs and piston crowns.
When the oiling system is functioning correctly the camshaft and crankshaft journals ride on a hydrodynamic wedge of oil that prevents the journals from ever touching the bearing inserts. This wedge is provided by the oil pump and companion components and its effectiveness depends largely on the oil’s viscosity, pump speed, proper bearing clearances, oil temperature, crankcase pressure, and bottom end components optimized for minimum drag. There are two basic lubrication systems currently utilized in racing engines: wet sumps and dry sumps. With either setup the primary components of the oiling system include:
- Oil Pump and drive mechanism
- Pump pickup
- Pan and associated baffles
- Oil filter
- Oil cooler if required
- Internal and external oil passages
- Windage control components
Typical wet sump oiling system incorporates an internally mounted gear-driven oil pump with windage tray and an extended submerged pickup in a deep-sump pan. Oil is picked up, pumped through the engine, and returned to the sump. (Courtesy Moroso Performance Products)
Moroso deep-sump big-block Chevy oil pan illustrates typical wet sump construction with full-length 7-inch-deep sump, metal oil stripper screen, and internal baffles to isolate and keep the pickup submerged.
Wet sump pans often require pump extensions and/or pickup extensions to properly position the pickup near the bottom of the sump.
Basic performance wet sump oiling systems usually incorporate a deeper, expanded-capacity oil sump to store the oil farther below the crankshaft assembly. A blueprinted stock pump or a specially designed race pump uses an extended pickup to scavenge oil from the bottom of the pan. (Courtesy Don Cooper, Reher-Morrison)
Racing wet sump pans often incorporate an extended kickout section on the passenger side of the engine. It provides an escape route for oil being flung off the crank assembly so it can’t rebound off the side of the pan, creating additional drag. (Courtesy Don Cooper, Reher-Morrison)
Engine designers and builders treat oil control as a major factor of engine design and construction. Considerable effort is devoted to ensuring that adequate pressurized oil is available to the engine’s moving parts at all times. Designers are also concerned with where the oil is stored, how it is retrieved from the engine, and how the engine’s oil supply is affected by moving internal components, oil temperature, pumping effort, and the dynamic influences of vehicle motion—all of which have a profound impact on the quality and consistency of a critical lubrication process that must not falter even for a second.
Of particular concern is the strict control or elimination of aeration and the formation of air bubbles in the oil supply (commonly known as cavitation ). Lubrication efficiency virtually ceases to exist in the presence of air bubbles and designers make every effort to control oil movement and exposure to conditions that promote oil foaming. Extreme turbulence caused by the rapidly spinning crankshaft assembly can grab oil returning to the sump and spin it into a nasty taffy-like mixture that exerts considerable parasitic drag on the engine’s internal parts. This crankcase condition, called windage, creates drag and has the potential to encourage the formation of air bubbles in the oil supply. This not only degrades oil pump and filter efficiency, it reduces the efficiency of the hydrodynamic oil wedge that supports moving components.
Aerated oil also tends to be less efficient at removing heat from components and its lubrication efficiency may become diminished to the point where important companion components undergo conditions of intermittent or insufficient lubrication. These include rocker arms, lifters, pushrod tips, valve guides, valve-springs, distributor gear, timing gears, and even the oil pump itself. In some cases these conditions may be partially helped by the improved lubricating qualities of synthetic oils, but only minimally. Moving parts need a filtered, cooled, and bubble-free supply of fresh engine oil at all times to ensure optimum performance and durability.
Wet Sump Systems
Wet sump oiling systems are the most commonly used oiling strategy in sportsman class racing and a few select professional classes because they are effective and relatively inexpensive. A wet sump system stores a reservoir of oil in the bottom of the oil pan and pumps it through the engine with an internally-mounted pump that is typically driven off the bottom of the distributor via a short driveshaft. An oil pump pickup attached to the pump extends to the bottom of the oil pan to pick up the oil. For best results the pickup is usually positioned within 1/4 inch off the pan floor to make certain it remains submerged.
This is the same basic oiling method used in most production cars, but it can be significantly enhanced with specialty components that improve oil control and increase power via drag reduction. Racing applications typically use higher capacity oil pans, racing oil pumps, extended pickups, windage trays, oil control kits, racing oil filters, and other components designed specifically to boost oiling efficiency under competition conditions. In some wet sump applications an external oil pump is used, allowing the windage tray or screen to extend the full length of the oil pan for more effective oil control.
Oil control is a key concern in a wet sump oiling system. The movement of sump oil initiated by constantly varying vehicle motion is a major contributor to intermittent conditions of oil starvation and the adverse effects of crankcase windage. The importance of steps to keep the oil pickup submerged in the sump oil supply at all times cannot be overstated. Under hard acceleration, oil climbs up the back of the oil pan and lateral acceleration tends to slosh the oil supply to one side or the other depending on the direction of turning. Even hard braking can initiate conditions where the pickup is briefly uncovered by oil movement and air is sucked into the pump to encourage aeration.
Various baffles, compartments, and trap doors within the oil pan sump section are employed to limit oil movement so the sump remains submerged under all dynamic conditions. Competition oil pans are constructed with sump extension compartments on one or both sides to increase capacity. Depending on the racing application pan baffles, compartments, and trap doors are configured to direct oil to the pickup at all times. On most oval track cars the oil tends to move to the outside (or right side) of the engine. With road racing cars, it moves to both sides depending on the direction of loading. Drag racing engines are typically concerned with preventing oil from stacking to the back of the sump and uncovering the pickup.
Windage Trays and Scrapers
Among the various oil control strategies, windage trays and crankshaft scrapers are a primary consideration. Sometimes they are an integral part of the overall pan design and often they are installed separately depending on the application and the specific control strategy employed. Some windage trays are mounted on extensions of the main cap bolts or studs and some are built right into the pan as permanent fixtures. The purpose of a windage tray is to mitigate the hurricane whipping effect of the spinning crankshaft and rods. In a high-RPM engine, windage can be strong enough to whip the oil supply in the sump into a stormy sea of aerated oil much like the ocean in a violent windstorm.
The windage tray serves to separate the primary oil supply from the eye of the storm and helps to preserve its liquid state while still permitting oil drainage via slots and channels in the tray itself. Some windage trays only cover part of the sump depending on the pan design and application. Other types employ louvers or expanded metal screens that help shield the oil supply while shearing oil from the spinning mass with minimal aeration.
Crank scrapers attempt a similar but more direct shearing by fixing their scraper edges very close to the crankshaft throws. Scrapers are typically hand fitted to provide the minimum required clearance between the scraper and the spinning crankshaft assembly. Generic-style scrapers that are fitted inside some pans do not follow the exact contours of the crankshaft and rods. These scrapers provide some benefit by shearing a given quantity of oil from the oil mass, but they are typically not as effective as a closely fit crankshaft scraper.
Side kickouts are an effective component of wet sump oil pans, but their efficiency is often compromised by the starter location, which prevents a full-length kickout to control oil coming off the rear crank throws. Internal windage control (right) features rear cutout for the pump and pickup, and a full-length curved windage tray incorporating louvers to direct oil back to the sump. (Courtesy Moroso Performance Products)
Scrapers also perform another important function by directing separated oil toward a special kickout section built into the pan on the upward side of crankshaft rotation (usually the passenger side). When the side of the pan is very close to the spinning crankshaft it encourages parasitic drag due to the proximity of the spinning oil mass. The kickout provides an escape route for oil being flung off the crankshaft. At higher engine speeds, increased mass inertia tends to toss the oil off the crankshaft toward the side of the pan in the direction of crankshaft rotation. Instead of hitting the side of the pan and rebounding into the oil mass to create more drag, oil is thrown into the kickout cavity where it drains back to the sump. Most scrapers support and encourage this effect and work in concert to separate crankshaft oil and minimize windage.
In many cases a well-configured scraper and kickout combination can be worth up to 20 hp, depending on the engine speed, the size of the concentrated oil mass, and the overall layout of the scraper/kickout combination. One problem with the effectiveness of this arrangement is that most GM engines and others have the starter located on the same side of the engine as the kickout, effectively limiting the length of the kickout to accommodate the starter. Shortened kickout cavities are the result and they lose some of the overall effect. Still, some kickout is better than none provided there is enough room in the chassis.
Wet Sump Oil Pumps
Wet sump oiling systems have been highly developed in part by tremendous demand for effective wet sump components that help curtail excessive expenses in sportsman applications. At a minimum this includes blueprinted and reworked factory pumps, high-efficiency internal and external pumps, custom extended oil pickup designs, and various support components designed to ensure the effectiveness of any wet sump system. Factory-style pumps and all external pumps are positive displacement designs, meaning the pump transfers the exact volume of oil that it takes in.
The different styles of pumps are distinguished by the type of gears used inside them—gerotors or spur gears. Spur gears are common to General Motors pumps while gerotors are found in most Ford and Chrysler applications. Spur gear pumps use one driven gear to drive a second freewheeling gear on a fixed shaft. Gerotor pumps typically use a four-tooth gear to drive a multi-cavity rotor that traps oil and transfers it in a similar fashion to a spur gear pump, but for the most part with greater efficiency at slower pump speeds.
The severe dynamics of race vehicle motion vary according to the application. In almost every case, wet sump systems are challenged to maintain control of the sump oil supply and keep it separated from the crank assembly at all times. Inertia typically prevails, thus all manner of internal baffles and trap doors are required to restrict unwanted oil movement. (Courtesy Moroso Performance Products)
If a wet sump pump is not completely submerged, the connection where the pump pickup enters the pump must be fully sealed to prevent the pump from sucking air above the sump level. Aftermarket racing pumps have special pickups designed for virtually every oil pan they offer. This is to ensure optimum pickup placement and performance under all operating conditions. If a factory-style pump is used, most builders disassemble it to deburr the gears and check the end clearance, which is typically limited to about .002 inch. Many blueprint the pump housing by grinding and straightening internal passages to ensure smooth uninterrupted oil flow with no cavitation.
Spinning a pump faster generally increases flow volume as long as steps are taken to prevent oil cavitation. As a rule this can only be done with an external pump where it is possible to change the pump’s drive ratio. Internal pumps gain flow volume with taller gears up to a point. The use of a big-block Chevy pump on a small-block is an example. The big-block pump has taller gears that transfer a greater volume of oil, but they also have more drag, which may be detrimental unless you absolutely need higher oil volume.
Savvy race engine builders consider the drag penalty and the loads incurred with higher oil pressure when contemplating higher flow volume or higher pressures. In most applications, 60 to 80 psi adequately meets lubrication needs. Wet sump pumps maintain pressure at any given flow rate by bypassing excessive oil. In the best case scenario, bypass oil should be limited so that the minimum volume needed to support the desired pressure is applied. Of course pressure should be limited to the amount required to fully support the hydrodynamic wedge in the bearing journals at maximum engine speed. To accomplish this, purchase the correct pump and pickup according to the manufacturer’s recommended specs.
Determining Oil Pump Clearance
Maintaining the proper clearance between the oil pump pickup and the bottom of the oil pan is critical to proper pump operation. The pump pickup must never suck air, hence the pump and/or pump pickup must be accurately located in reference to the floor of the pan. With the oil pan removed, this measurement is easily taken using a combination square with a sliding rule. Position the square against the block’s pan rail and slide the rule to measure the distance to the bottom of the pickup. Then lock the rule in place. Without changing the setting, check the depth of the oil pan from its rail down to the bottom. The difference indicated should be a 1/4- to 3/8-inch gap between the end of the rule and the pan’s bottom. A clearance greater than 3/8 inch may result in aerated or inadequate oil flow, while clearances less than 1/4 inch could disturb or restrict oil flow patterns and cause cavitation.
Drive systems vary considerably depending on the application. Most manufacturers have auxiliary hardware such as this water pump mounting plate for a Moroso alternator and vacuum pump. Appropriate-drive mandrel components are also required to properly position the drive belts.
Dry sump plumbing is sometimes difficult. This system uses a single large -16 AN return line to the tank instead of more typical multiple lines. Where the chassis configuration permits, it also mounts directly to the oil pan, eliminating the clutter of external lines from the pan to the pump.
Some builders claim the pump can draw hard enough to close up the gap if the pan material is too thin. A common trick is to weld a small 3/8-inch metal tab to the bottom of the pickup to position it accurately. This works very well, but it requires careful pre-positioning of the pickup in the pump before final assembly. Once this is done many builders like to tack weld the pickup to the pump or even braze it in place. If you choose to do so be sure to remove the bypass spring to prevent heat damage and recheck the pump mating surfaces for distortion that might affect proper gear alignment and rotation.
Dry Sump Systems
Dry sump oiling systems store their oil supply in a separate tank leaving the oil pan virtually dry because multiple scavenge pumps suck it out as fast as possible. An external pump assembly incorporating multiple scavenge stages (typically three, four, or more) sucks oil out of the shallow pan and delivers it to the storage tank. The pressure section of the pump sucks oil from the tank to pressurize the engine’s oiling system. A single pressure stage is normally used to return oil from the tank to the engine while the scavenge section may incorporate anywhere from two to six pickups, some of which are often used to scavenge oil from the valve covers or the lifter valley beneath the intake manifold.
A dy sump’s primary advantage in a racing engine is its ability to make more power. With minimal oil in the pan, the rotating system is not burdened with the weight and parasitic drag of the excess oil whipped up by the spinning crank. With no internal pump, the windage tray or screen, which normally isolates sump oil from the rotating assembly, can run the full length of the oil pan, keeping the rotating assembly free of windage so it spins more easily and delivers more power. Crankcase vacuum created by the dry sump scavenge stages also improves ring seal and encourages more power.
Dry sump systems provide increased oil capacity in a separate reservoir, more consistent oil pressure, and the ability to easily adjust oil pressure. Since the pan doesn’t store any oil, it can be made relatively shallow to permit lower engine placement in the chassis to improve handling and weight distribution. Separate plumbing provides the opportunity to run a small in-line filter on each scavenge stage for maximum filtering effect. In some cases manufacturers also offer scavenge manifolds that accept scavenged oil from two or more pickups and route it through a single filter prior to delivery to the storage tank. In either case, the opportunity to send the oil through a cooler along the way presents itself.
High-end systems like this Pro Mod setup incorporate up to five scavenge stages, some of which are dedicated specifically to pulling a vacuum on the crankcase. (Courtesy Don Cooper, Reher-Morrison)
Sometimes a manifold arrangement is also incorporated on the pressure stage to send pressurized oil to the engine at different points such as front and rear pressure entry ports.
It’s pretty normal to use two or more scavenge ports on the oil pan. They are typically located as near the floor of the pan as possible and their location is often further dictated by the specific racing application and where the designers feel is the best point to scavenge the oil most effectively under actual racing conditions and the associated g-loading.
Drag racing pans tend to concentrate sump pickups toward the rear of the pan while oval track setups typically scavenge from the right side of the pan. In either case the actual pickup fitting may be on the opposite side of the pan with an internal extension pickup that helps ease plumbing problems in restrictive chassis arrangements.
Road racing, off-road racing, and many marine applications usually have the scavenge points located near the center of the pan for maximum effectiveness under constantly changing conditions. Some manufacturers actually mount the pump assembly directly to the oil pan to eliminate plumbing restrictions. This may be advantageous in certain chassis configurations.
There is a broad choice of steel or aluminum pans, either of which may present advantages depending on the application. Some builders also modify commercially available pans to suit their own particular requirements.
Choosing a Dry Sump Pump
A leading manufacturer of race oiling systems, Moroso offers a full range of dry sump oiling system components all engineered to be fully compatible with one another. This helps you select the best combination of equipment to avoid potential problems that may occur when “mixing and matching” components from various manufacturers. According to Moroso, you need to consider the following before choosing a standard or custom oil pump:
- Weight of the oil
- Operating temperature range
- Oil consumption at idle
- Oil consumption at operating range
- Desired vacuum level
Pump selection requires a builder to determine the number of scavenge and pressure stages required for the application, the type of gears or rotors for a desired pump drive ratio, drive belt type, and mounting configurations according to operational chassis requirements. Further consideration must be given to pump materials, with coated aluminum being the most popular. Some applications also incorporate a cable-drive adapter to operate a remote mechanical fuel pump. Moroso, Barnes, and Weaver Brothers all offer high-end race pumps incorporating internal manifolds to minimize plumbing and space requirements.
Determining the required number of scavenge stages requires careful contemplation. In addition to scavenging oil from the sump, oil may also be taken from the valve cover or from the lifter gallery. Some dedicated racing engines route upper engine oil directly to an internal scavenge gallery so it never enters the sump at all. Multiple stages increase pumping volume and vacuum in the crankcase. More stages means that the pumps are sucking a lot of air in addition to oil. Air and other vapors must be separated from the oil before it can be routed back to the engine in pure liquid form.
This illustration shows the major components of a dry sump system and how they are plumbed for maximum effectiveness. Most systems are plumbed this way or similarly depending on the application. The primary components include a multi-stage dry sump pump, drive mandrel with pulley and drive belt, racing oil filter, storage tank, breather tank, oil pre-heater and the accompanying plumbing that typically incorporates braided steel hoses, in-line filters, and the appropriate AN fittings to connect it all together. (Illustration Courtesy Moroso Performance Products)
The dry sump pump incorporates a Gilmer belt-drive pulley on the front with multiple scavenge and pressure stages stacked behind it. The rear stage is the pressure stage that pumps oil from the tank to the engine. The front two lower fittings are scavenging stages attached to the dry sump pan. Both of them return scavenged oil to the tank via the single -16 outlet on top at the front. The unit hanging down at the rear is for oil-pressure adjustment.
With appropriate filter attachment, the CV Products remote oil filter mount offers a convenient way to plumb a filter between the dry sump pres¬sure stage and the engine. It features dual- or single-inlet usage and it incorporates a fitting for reading oil temperature.
Dry sump pumps typically mount on the lower left or right at the front of the block with a pivot bolt for easy belt-tension adjustment.
Some applications incorporate a pump-driven air/oil separator to precondition scavenged sump oil on its way to the storage tank. The tank itself is configured to separate air and oil vapors, bleeding it off to a separately vented tank.
Oil entering a circular dry sump tank from the scavenge stages is introduced tangentially with a swirling motion that encourages air and vapor to rise to the vent opening while oil drains to the storage section via additional baffles and separators. This design is very effective at eliminating aeration and collecting only liquid oil in the bottom of the tank.
As a rule, a taller tank is more effective and requires the least amount of internal baffling and oil control. Shorter tanks that may have space limitations often require more baffling and more complicated air separation. Some of this also speaks to the builder’s preferred oil volume. Generally small-block engines require less volume than big-blocks, but the requirement is also tempered by the final application in terms of available oil capacity and the ability to cool the oil effectively. Where a drag car with a short event duration may work well with a small 1½-gallon tank, endurance applications generally require as much as 4 to 5 gallons. This is true for speedway operation, off-road racing, road racing, and some marine endurance applications like offshore power boat racing.
Pump Speed Drive Ratios
A dry sump system can regulate oil pressure according to pump speed via the combination of belt circumference and pulley sizes to achieve the required drive ratio. Manufacturers offer a broad choice of pulley sizes to accommodate a wide range of ratio options and crankshaft-to-pump-shaft centerline dimensions. With a given belt circumference, you can position the pump farther away from the crankshaft centerline using smaller-tooth pulleys with a specified drive ratio. By using larger-tooth pulleys for the same ratio, the area from centerline to the crankshaft can be reduced, but in either case they have the same drive ratio.
Builders with a good working knowledge of the requirements and chassis arrangement can consult the manufacturer to achieve the drive ratio and pump position that accommodates their pressure/volume and chassis fitment requirements.
Oil Pan Installation
A common-sense approach to pan installation suggests starting with a thorough cleaning and inspection for damage or potential leaks from cracks or other damage. While unlikely with a new pan, recall the prime directive of race engine construction: Check everything and then check it again. Use OEM-quality gaskets or the equivalent and a quality sealer. Apply a small dab of silicone sealer at each corner where the rubber seal meets the rail gaskets. Moroso technicians recommend installing the pan with the engine in the upright position if the pan incorporates internal trap doors. This prevents the doors from sticking open accidentally.
Minor rocking (approximately 1/4-inch is acceptable) may be encountered when installing the pan. This is normal even on high-quality pans; it stabilizes once the pan is tightened. Start all the bolts before you tighten any of them, or if you are using studs, install all of the nuts loosely.
This dry sump oil pan has two pickup points on the side of the pan and one each at the front and rear in case the side pickup encounters chassis fitment issues. The tubes inside the pan are connected to the pan outlets. They have slots in the bottom to pick up sump oil from the bottom of the pan.
All race engines should incorporate a Filtermag as part of their overall oiling strategy. The Filtermag prevents contamination of the oil supply by trapping all metal particles inside the filter canister.
Secure the mounting bolts or nuts in each corner, tightening them to less than 50 percent of final torque. Then move to the center bolts tightening them in an alternating “X” fashion working toward the ends of the pan in a circular motion similar to that used for head gasket torquing.
Repeat this procedure at 75- percent torque and then at the final torque setting to seat the pan correctly. Thread sealer, such as Loctite, is recommended on all fasteners and most true race applications may also require safety wiring.
Crankcase Vacuum Pumps
It is common practice to use an auxiliary vacuum pump to create vacuum in the crankcase. This helps control windage but its primary purpose is to reduce pressure below the piston rings so you can run lower tension rings that significantly reduce friction in the cylinders. Racers used to accomplish this with a “pan-evac” system consisting of one-way check valves and a vent whistle assembly installed in each header collector at a 45-degree angle to the direction of exhaust flow. A hose running from an air/oil separator on each valve cover to the check valve allowed the collector to pull a slight vacuum on the crankcase. Once the beneficial effects of this were confirmed it was found that more vacuum worked even better. Vacuum pumps were the next logical step.
Considerable research has determined desirable vacuum levels for various applications and the appropriate components to achieve it. Multi-stage dry sump pumps are often used to accomplish a certain level of vacuum and these may or may not be supplemented by a dedicated external vacuum pump. Many wet sump systems also incorporate an external vacuum pump with good results. Baffling is required at the suction side to separate oil and vapor and a breather is installed at the outlet side to accumulate any oil that migrates through the pump.
Optimum vacuum levels are a matter of considerable discussion. Leading engine builders and race teams all confirm that 10 to 14 inches of vacuum on a wet sump system creates additional horsepower while minimizing oiling-related problems. Dry sump engines function optimally in the range of 18 to 22 inches. While a good system with multiple pumps is normally capable of achieving greater vacuum levels, it is best to consult the pump manufacturer and your ring supplier if higher levels of vacuum are desired.
A Filtermag attracts all metal particles that pass through the filter housing. As shown here the captured material aligns itself according to the magnetic field created by attaching the Filtermag to the outside of the filter canister.
Manufacturers such as Moroso carry a variety of vacuum relief valves to adjust the maximum amount of vacuum an engine makes. The best time to check vacuum and oil pressure together on a drag race application is during the trans-brake check. At staging RPM, monitor vacuum and oil pressure to determine the state of the system. For other applications it is advisable to incorporate a data logging port to constantly monitor crankcase vacuum for comparison to other engine conditions that are also being recorded.
Vacuum levels depend on pump speed. As a major supplier of race engine vacuum pumps, Moroso recommends starting at 50 percent of engine speed. If more vacuum is required at lower engine speeds (at idle or staging RPM) or across the overall power range of the engine it is necessary to increase the pump drive ratio according to your specific requirements and the recommendations of the pump manufacturer. Some pumps are limited to 6,500-rpm shaft speed while others can turn up to 8,000 rpm so make certain you are using the correct pump and drive ratio.
Pump inlets are best attached to the front or top of a valve cover using a fitting with a built-in baffle that allows a small amount of oil to flow to the pump to lubricate the pump vanes.
Oil Accumulators for Racing Engines
Oil accumulators are independent auxiliary oil storage tanks connected to an engine’s oiling system that have pressurized air on one side of a moveable internal piston, and engine oil on the other side. If engine oil pressure drops or fluctuates due to oil surging away from the pickup during hard acceleration, severe cornering, or hard braking, the accumulator instantly provides a temporary supply of oil to the engine. When the fluctuation is over and full pressure is restored, the engine’s oil pressure forces this reserve of oil back into the accumulator. Under normal engine oil pressure the accumulator is pressurized and refills automatically to reload the temporary oil supply. Some drag racing applications have successfully used accumulators to free up horsepower by lowering the oil level in the sump and relying on the accumulator to maintain adequate pressure if required.
On Moroso accumulators, the end cap on the air side has an air gauge and Schrader valve; the oil side has a 1/2-inch NPT fitting for plumbing into the oiling system. Accumulators require a valve assembly to function properly so they are equipped with a manual ball valve. The valve has to be manually opened before starting the car to pre-oil the engine (offering surge protection) while the vehicle is in use, and closed when the engine is turned off.
Moroso offers two styles of optional electric valves with its accumulators: A solenoid valve (electric) allows remote control of the accumulator. Solenoid pressure valve kits are the best performing for competition vehicles and are offered in different oil pressure ranges of 15 to 24 psi, 35 to 40 psi, and 55 to 60 psi discharge and refill. They have all the benefits of the solenoid valve but with quicker reaction times because the solenoid pressure valve allows only the necessary volume of oil to be released for faster filling and discharging. An internal sensor electronically activates when engine oil pressure drops below normal.
Independent tests have shown over 85 percent of engine wear is caused by starting an engine, and that these “dry starts” cause premature engine wear. Accumulators prevent cold-start scuffing by pre-oiling the engine before startup. Most race applications require a 3-quart-capacity accumulator for optimum protection. A single line is required to plumb it into the oiling system (either tee’d into the return line of an oil cooler or remote filter). An adapter mounts between the engine’s spin-on oil filter and the engine or, in many cases, runs directly into a pressurized oil gallery port in the engine block.
Engine builders have developed many tweaks and modifications over the years, some of them specific to the oiling system. Most involve increasing or decreasing oil flow to selected components as operating conditions warrant.
Among the more common modifications are efforts to restrict oil flow to components that don’t necessarily require full-time oiling. The intent is to limit oil flow and lubrication in areas where it may increase parasitic drag or to minimize the amount of oil dripping on the crankshaft and rotating assembly. These may include roller rocker arms and other upper engine components that require only minimal lubrication. The reverse of this might include piston pin oilers designed to spray additional oil beneath the piston crown to lubricate the wrist pin and cool the piston crown.
Another example is a block equipped with roller cam bearings that obstruct the camshaft oiling holes and receive lubrication strictly by splash. In many cases the oiling supply to roller lifters and roller rockers is significantly reduced to minimize friction. When oil to the top end is reduced, there is less overall drainage through the crankcase, which helps to mitigate the effects of windage. Needle bearings and rollerized components help support these efforts when top-end oiling is restricted through the use of commercial restrictors in the oil galleries or special metered orifices installed to restrict oil flow. Priority main oiling, as found in modern race-bred blocks, supports this by directing oil to the mains first and then supplying other components as needed.
An accumulator is a pressurized remote oil supply that provides temporary full-pressure oiling prior to engine startup or whenever a pump issue causes an interruption or complete failure of the oil supply.
Non-race Chevy blocks typically use commercially available oil restrictors inserted in the back of each lifter gallery to limit upper engine oiling. The same effect can be accomplished by installing new metered jets in the gallery. These help support the reduction of parasitic drag including pumping effort required of the oil pump and subsequent loading against the distributor gear, which may have negative consequences for precision engine timing.
However, there are trade-offs. Too little oil upstairs may negatively affect valve guide and valve spring life and this must be weighed against the lifespan of these components versus the overall event duration of the specific racing application. It may not be of serious consequence in a drag race, but it may initiate unwanted problems in a durability application such as a 6- to 24-hour endurance race. In this case commercially available valve covers with integral spring oiler tubes usually solve the problem.
Efforts to isolate and limit lifter valley oil from draining onto the camshaft include installing tall standoff vent tubes in the valley drain holes and/or isolating the area completely by installing a sheet-metal block-off plate with epoxy. The idea is to force excess oil to drain at the front or rear of the block so its exposure to the crank throws is limited.
Some builders don’t mind oil draining via the timing cover; others epoxy sheet-metal dams in the front drain holes to force all oil to the rear of the valley where it must drain on the rear main throw and distributor, or in the case of a dry sump, be evacuated at that point. The intent here is to isolate lubricant, not to prevent equalized pressure within the crankcase itself. While oil must be closely controlled, lifter valley pressure must remain equalized to prevent end gasket failure due to excessive crankcase pressure or vacuum (as the case may be).
Many specialized race blocks isolate the camshaft tunnel completely and provide separate internal drain paths leading directly to the sump area so none of this oil can affect the spinning crank.
Baffling the Crankcase
Builders often try to isolate the individual crankcase bays of paired cylinders to further reduce oil contamination. This is done in the form of baffles or dams that restrict oil motion without compromising bay-to-bay breathing where higher crankcase pressure might be created under select cylinders. The efforts most often accompany dry sump oiling systems where an individual scavenge port is assigned to each individual bay of the oil pan.
These efforts are often application specific and you must weigh the alternatives both positive and negative before finalizing specialized modifications that have the potential to dramatically aid crankcase breathing and oil control or just the opposite if proper care is not exercised.