Efficient lubrication plus reduction of parasitic power loss.
By Mike Mavrigian
A street engine, and many race engines, utilize a "wet sump" system to deliver pressurized oil to the engine's internal rotating and reciprocating assemblies. Engine oil is stored in the oil pan sump (the big reservoir section of the pan). The oil is picked up by a mechanically driven oil pump, which obtains the sump's oil via a submerged oil pickup. As the pump rotates (the pump runs whenever the engine runs, since it's driven by the crank or indirectly via the distributor drive), oil is pressurized and distributed from this main source throughout the engine as oil is distributed through the oil passages in the block, crank journals, main bearings, rod bearings, and, eventually, to the valvetrain. Although this system does deliver oil to all required areas, the oil must be pushed through all of these passages to eventually route to the upper end of the engine. The delivered oil is then free to drain back to the sump, with delivery and drain-back serving as an ongoing cycle during engine operation. A "dry sump" system takes a different, and much more direct approach. This uses an externally-mounted oil pump, which takes advantage of external plumbing to directly deliver oil to the engine. The oil pan does not feature a sump reservoir. Instead, the dry sump pan serves only as a containment cover and as a location from which oil can be returned to the reservoir. The oil reservoir (oil supply) is a remote container (usually mounted in the cockpit or other convenient location in the race vehicle). In very basic terms, the external pump pulls oil from the remote reservoir, and then pushes the oil (under pressure) to wherever the plumbing directs it. In this manner, oil can be directly sent to the main bearings through a block port, oil can be delivered directly to the valvetrain with one or two plumbed hoses (depending on the application) and oil can be directly delivered to a turbocharger, etc. Dry sump pumps are offered in stages depending on how many direct-delivery and return (scavenge) routes are required. The advantages include immediate oil delivery to specific areas and elimination of oil starvation caused by angle and centrifugal forces (when the race car accelerates, brakes or turns), which may momentarily expose an in-the-pan oil pump pickup, allowing air (not oil) to travel throughout the block. In other words, the potential for oil aeration is eliminated. Since the scavenge section(s) of the dry sump pump pull oil from the dry sump pan, this creates a vacuum, pulling excess oil from the surfaces of the crank and rods, reducing parasitic drag (which means more efficient use of engine power). When plumbing a dry sump system, size requirements may vary somewhat, but a general rule of thumb is to use -10, -12 and -16 hose, fittings and hose end sizes (for some turbo applications, a -6 hose size is recommended). Generally, a larger size is required for the return hose that runs out from the pump to the remote oil reservoir (for instance, if -12 hoses are used for all feeds, a -16 hose would be used for oil return to the reservoir). Although a dry sump oil pan will feature threaded bungs to accept suction line fittings (where drainback oil is pulled by the pump), plumbing to the block or other areas may require drilling and tapping or the purchase of special adapters. Typically, if an adapter is needed to feed oil to the block's main galley (at the stock oil filter location, for example), aftermarket adapters are readily available for all popular blocks. By the way, if you're using the OE filter location for oil feed, you'll need to remotely locate an oil filter. An externally mounted dry sump oil pump is most commonly driven by a notched belt (toothed belt often referred to as a Gilmer belt), directly from the crankshaft snout (a pulley is installed on the crank, with the belt connecting the crank pulley to the pump pulley). Dry sump pumps, via the proper pulley diameters, are generally driven at about half of crankshaft speed. Dry sump pumps driven by the nose of the camshaft are also available, with the pump mounted on the face of a special timing cover.
DRY SUMP SYSTEM ADVANTAGES
- Superior consistency of oil pressure
- Oil isn't pushed away from the oil pickup during severe turns, acceleration or braking, as may occur with a wet sump system
- Adjustable oil pressure
- Increased oil system capacity
- Shorter profile pan, allowing engine to be mounted lower in chassis for lower center of gravity.
- Increase in engine power
- Positive oil delivery to critical areas of the engine
- Cooler oil supply (since the oil is quickly returned to the remote reservoir instead of being stored in the hot oil pan)
A dry sump pump features a pressure section and a scavenge section. The pressure section delivers oil to the engine, while the scavenge section pulls "leftover" oil from the dry sump pan and sends it back to the remote oil reservoir. Dry sump pumps are built in "stages, with one pressure section and one or more scavenge sections. The additional scavenge sections (as few as one, as many as 6) allow oil to be scavenged more quickly and efficiently from specific areas of the engine, instead of waiting for the oil to be drawn down into the pan for scavenge pickup. A typical 2-stage dry sump pump features 1 pressure section and 1 scavenge section. A typical 3-stage dry sump pump features 1 pressure section and 2 scavenge sections. A typical 4-stage dry sump pump features 1 pressure section and 3 scavenge sections. A typical 5-stage dry sump pump features 2 pressure sections and 3 scavenge sections. A typical 6-stage dry sump pump features 2 pressure sections and 4 scavenge sections. A typical dry sump oil system features a host of components including:
- Dry sump pump
- Dry sump pump pulley
- Toothed pump drive belt
- Pump fittings (male -AN 37-degree flare to accept -AN hose ends)
- Pump mounting bracket
- In-line screened oil filter(s)
- Remote in-line oil filter and filter mount
- Remote-mounted oil tank
- Breather (separate or on-tank)
- Oil filter block-off plate for engine block
- Required -AN hose assemblies
The dry sump system oil tank simply serves as the primary oil reservoir. The tank receives the oil scavenged from the outlet ports of the dry sump pump. Once the oil enters the tank's inlet fitting, the oil hits an internal "splitter" that directs the oil in a specific stream. After hitting the rolled inner tank wall (this softens the impact of the oil) it rolls onto an upper baffle, allowing the oil to flow out in a thin sheet, which promotes the release of air that might be trapped in the oil. The oil then falls into the reservoir, waiting to be pulled out and recycled through the engine. A large portion of the tank volume is air, which exceeds the volume of oil being pulled from the pump. To allow air to escape, the tank must be vented, which also benefits the system by lowering atmospheric pressure in the crankcase. Dry sump tanks are available in capacities ranging from 1 gallon to 5.5 gallons.
This overhead view shows the pump side-mounted to the block. The toothed Gilmer belt connects the small diameter toothed crank pulley to the pump pulley. The dry sump pump runs at approximately half of the crank speed. Notice the two hose ends on the top of the pump. The larger -16 will be plumbed to the upper port of the reservoir, serving to return oil from the pump's scavenge back to the tank. The -12 will be plumbed to the block's main oil port to feed the engine.
The -16 hose shown here plumbs scavenged oil from the pump to the remote reservoir. A fitting/hose connection at the bottom of the reservoir is the feed line from the reservoir to the pump. Note the oil delivery -12 hose to the oil filter adapter on the block. The reservoir shown here was mounted on our shop's engine stand for display purposes. The reservoir will be mounted in the race car cockpit area (obviously with longer hoses).
Quick-connect couplers allow quick connection/disconnection of oil hose assemblies without loss of oil. The Jiffy-Tite coupler shown here features valving that shuts off when the connection is uncoupled. Use of these quick-connect couplers allow for faster engine removal with no oily mess.
When routing your plumbing hoses, make sure they don't interfere or rub on any moving parts. Here the two hose ends are installed at a sufficient angle to prevent the hoses from touching the timing belt, and the hoses are secured together with an aluminum hose separator.
Dry sump pumps are built in stages. The ports marked "IN" are for scavenge hoses and oil feed from the reservoir. The ports marked "OUT" are for pressure output from the pump and for return to the reservoir. Pulleys are keyed and provide a positive retention onto the pump drive shaft. (Photo courtesy of Barnes.)
In this plumbing hookup, we installed -12 male AN flare adapters to the pan to accept -12 hose ends. For the scavenge hose being installed in this photo, we chose a straight hose end for the pan connection and a 45-degree hose end at the pump. The capped fitting seen on the scavenge side of this pump will be used to connect to the reservoir's bottom port to pull oil from the tank to the pump. Due to the range of hose end shapes available, it's easy to create direct and tidy plumbing regardless of the engine configuration.
Soft aluminum wrenches prevent gouging the hose end couplers, and prevent damaging the hex corners. CAUTION: If an engine fails (by that we refer to any problem that allows metal debris to enter the oiling system), don't neglect the dry sump system during the rebuild process. The external oil pump must be disassembled, cleaned and inspected for damage (in-line filters can be plumbed in-line in the oil return lines during system installation, which is always a good idea, But even if a filter is present, the pump should still be inspected). Naturally, the remote oil reservoir should also be cleaned. However, many people tend to overlook the hoses (and a remote oil cooler, if present). If you suspect metal contamination, although you may try to flush and clean all of the hoses, if you're dealing with hoses that you can't also visually inspect (long hose or hose fitted with angled hose ends), the safest route may be to replace the hoses. That's a call you'll need to make on your own, but be aware that random debris might be lodged in the hose inner wall. If you're certain that the hose is clean, by all means feel free to re-use it. If you have any doubts, though, spend the money to replace it. As far as external oil coolers are concerned (and this holds true for any remote cooler, whether it's for the engine, transmission or axle drive), if you suspect that metal debris has entered the cooler, replace the cooler. Unless you have access to an X-ray machine, you'll never be certain that the cooler tubes are clean. If you reuse a contaminated cooler, you're asking for trouble because the debris can dislodge and run into the engine. Considering the cost of a cooler (even the most expensive type) versus the cost of the engine, it's good insurance to toss the suspect cooler and buy another.
Machined billet aluminum oil filter block on a Honda. This engine was fitted with a dry sump oil system. Note the finger pointing to a round plug. This was the OE location for a crankcase breather. Since the dry sump system pulls vacuum in the oil system, the block breather wasn't needed, so we made a press-in aluminum plug on the lathe. All photos by author unless otherwise noted.
5-stage dry sump system. (All example plumbing illustrations courtesy Aviaid)Sources
DRY SUMP COMPONENTS/SYSTEMS ARE DRY SUMP SYSTEMS (dry sump pans) For more information, dial 1-800-652-0406, ext. 13401 Online, visit www.precisionenginemag.com/info/13401 AUTO VERDI RACING OIL PUMPS (dry sump pumps) For more information, dial 1-800-652-0406, ext. 13402 Online, visit www.precisionenginemag.com/info/13402 AVIAID OIL SYSTEMS (dry sump oil systems) For more information, dial 1-800-652-0406, ext. 13403 Online, visit www.precisionenginemag.com/info/13403 BARNES DRY SUMP OIL SYSTEMS For more information, dial 1-800-652-0406, ext. 13404 Online, visit www.precisionenginemag.com/info/13404 BILLET FABRICATION (wet and dry sump pans) For more information, dial 1-800-652-0406, ext. 13405 Online, visit www.precisionenginemag.com/info/13405 CANTON RACING PRODUCTS (pans, accusumps, filters) For more information, dial 1-800-652-0406, ext. 13406 Online, visit www.precisionenginemag.com/info/13406 CHAMP PANS/JR MFG. For more information, dial 1-800-652-0406, ext. 13407 Online, visit www.precisionenginemag.com/info/13407 DAN OLSON RACING PRODUCTS (aluminum dry sump pans) For more information, dial 1-800-652-0406, ext. 13408 Online, visit www.precisionenginemag.com/info/13408 JOHNSON'S HIGH TECH PERFORMANCE (dry sump oil pumps) For more information, dial 1-800-652-0406, ext. 13409 Online, visit www.precisionenginemag.com/info/13409 MILODON INC. (pumps, pans) For more information, dial 1-800-652-0406, ext. 13410 Online, visit www.precisionenginemag.com/info/13410 MOROSO PERFORMANCE PRODUCTS (pumps, steel and aluminum pans) For more information, dial 1-800-652-0406, ext. 13411 Online, visit www.precisionenginemag.com/info/13411 PATTERSON ENTERPRISES (dry sump oil tanks) For more information, dial 1-800-652-0406, ext. 13412 Online, visit www.precisionenginemag.com/info/13412 PETERSON FLUID SYSTEMS (dry sump pump systems) For more information, dial 1-800-652-0406, ext. 13413 Online, visit www.precisionenginemag.com/info/13413 STEF'S PERFORMANCE PRODUCTS (B&B pans) For more information, dial 1-800-652-0406, ext. 13414 Online, visit www.precisionenginemag.com/info/13414