When it comes to engine oiling systems they’re generally divided into two categories: dry sump and wet sump. With the exception of ultra-high performance sports car likely to see track use, most OEM oil systems are classified as wet sump. However, in exotics and in race cars, where allowed, the choice is a dry sump system. So what are the pros and cons of a dry sump system?
Dry Sump versus Wet Sump
First, let’s consider the actual advantages of a dry sump system over a wet sump system. First, the oil in the crankcase can be virtually non-existent, as it’s drawn away by the scavenge pumps, which use negative pressure to draw oil out of the bottom of the engine and into the outboard oil tank. The problem faced in a wet sump engine is an issue called windage.
Windage is caused by the pistons moving up and down creating a swirling environment in the crankcase. While the air alone does increase drag on the crankshaft, having oil in the sump results in oil being sucked up into this swirling vortex which adds a significant additional amount of horsepower-sucking drag to the mix. In race engines that have to run a wet sump pan, windage is reduced by various trays, panels, and traps, but they’re not nearly as effective as a dry sump system.
Second, there’s more oil in the system when you add together what in the engine, the lines, the pump, the cooler, and the oil tank, so you’re far less likely to starve any part of the engine for oil during hard cornering.
Third, as described in the windage section, the engine churns the oil until it’s more frothy than a smoothie. Oil that’s pumped full of air bubbles isn’t an effective lubricant so part of the duty of the oil tank is not just to hold incremental oil but to also give the air a chance to separate from the oil before the oil is fed back back into the engine.
Fourth, as a dry sump system doesn’t require a traditional deep oil pan, just a cover for the bottom of the engine with fittings for the oil lines, the engine can sit further down in the chassis, lowering the center of gravity (and given the weight of most engines, it’s not an insignificant advantage).
Why Are Dry Sump Systems Not More Prevalent?
OK, so if a dry sump oiling system is so superior, why isn’t it fitted to every new car? There are two reasons. One is cost. The other is that most cars driven on the street don’t require a dry sump oiling system. They simple don’t see the conditions that race track use places on an engine’s oiling system, so for the most part a dry sump system would be superfluous.
Integrating a Dry Sump Oiling System
So, if you’re competing in a class that allows for the replacement of the OEM wet sump with a dry sump oiling system, how do you go about making the change? Thankfully. we have an example right here with the Project T-Rex, where an enormous 5.0L Ford Coyote V8 is being stuffed between the frame rails of our 1974 British TVR 2500M sports car. In this case, not only are the advantages of a dry sump oiling system needed as the car will be track-driven, but there’s also a space issue in the tight engine compartment plus the engine needs to be as low as possible to clear the hood.
Mighty Coyote And Dry Sump
Our Coyote, which has been upgraded from stock by Livernois Motorsports, now features Manley Performance 11:1 Platinum Series pistons fitted with Total Seal rings, Manley H-beam forged steel rods, a Comp cam, Livernois Motorsports CNC-machined heads and Borla eight-stack EFI with FAST controls and is anticipated to produce 550-600 flywheel HP on the dyno at Livernois. It’s also being tuned to provide the rapid throttle response needed to optimize post-apex acceleration on the track. The last thing we want is for all the hard work and expensive parts that went into building the engine to go up in smoke at the first autocross.
With an engine of this caliber stuffed within a full tube-frame chassis with a modern, sophisticated suspension, we’re certain to be seeing the types of sideloadings that require a dry sump system. But where to start? Fortunately, John Schwarz of Aviaid Oil Systems made it all happen.
Roots Back to Bruce McLaren
Relative newcomers to motorsports may not be familiar with the company or its heritage, but it was Aviaid who pioneered the use of dry sump systems in auto racing, beginning with the 620 horsepower McLaren M8A Can Am race car. Aviaid was also the company that Carroll Shelby relied upon to provide the oiling systems for his Le Mans-winning Ford GT40 and Cobra race cars 50-plus years ago.
Dry Sump Oil Pan and Pumps
However, it’s Aviaid’s contemporary technology that’s providing an ample supply of ‘life blood’ to the Livernois Motorsports-built Coyote nestled in T-Rex’s frame rails. A good example of this is the low profile 1.75″ deep CNC-machined billet aluminum oil pan that facilitates the lowest possible engine placement. It comes with provision for five scavenge pick-ups, but T-Rex’s normally aspirated engine will only require three of them. The three scavenge lines feed into an Aviaid four-stage Series 1 pump, which features an internal manifold to merge the flow from three sections into one outlet that delivers the heated oil to the top of the 10-quart dry sump oil tank that’s located directly in front of the engine.
From there, the aeration caused by crankcase windage is significantly reduced in the fully-baffled outboard oil tank. The oil is then fed out of the tank to be cooled and filtered. As dry sump pumps go, the four-section design is more than adequate for a normally aspirated 5-liter engine. The three scavenge sections are 1.50″ wide and made of aluminum, while the 1.50″ wide pressure section is steel, which allows for running tighter impeller-to-housing clearances as steel is less prone to expansion from heat.
Aviaid offers sections in widths ranging from 0.60″ to 2.00″ in width, as well as pumps with up to 9 sections. This particular pump is a gear unit, though Aviaid also offers a Roots-type impeller setup. There are also Gerotor style pumps on the market.
Integrating A Pressure Regulator
A built-in pressure regulator on the pump maintains adequate pressure, though it’s the volume of oil moving through the engine that’s most important. According to Aviaid’s Schwarz, “It is the volume delivered by the pump that determines pressure.” Schwarz added, “We offer seven different segment sizes, each providing a different amount of oil delivered with each revolution of the gear set. The goal is to deliver the appropriate amount of oil to the engine to deliver the pressure set-point desired. Too little oil and you won’t be able to achieve the desired oil pressure at speed. Too much oil and you won’t be able to control oil pressure at peak RPM.”
The regulator assembly can adjust pressure within a range, but once that capacity to bypass oil is reached, pressure will build uncontrollably. “For scavenge sections the number of sections and the size of those sections is varied for efficient scavenging of oil from the engine. Most engines work well with two scavenge sections, typically of the same size as the pressure section. A third section may be added if the pan is exceptionally big, or cylinder heads tend to trap oil.
“Additionally most of what the scavenge sections remove from the engine is air. Provided sufficient displacement exists in the pump, more air can be removed from the crankcase than is pumped into the engine through the cylinders, pressure in the crankcase can be reduced below atmospheric, yielding further benefits resulting from additional reductions of parasitic losses and increased piston ring sealing efficiency,” Schwarz stated.
While Aviaid has pump mounts for standard Coyote applications, the close quarters in T-Rex necessitated fabricating an adapter plate for the passenger side of the block and employing one of Aviaid’s myriad mounting blades to provide optimum clearance as well as the ability to adjust belt tension.
Driving a Dry Sump Pump
An ATI Super Damper is also an important part of the equation, not only for controlling harmonics, but for providing a serpentine drive for the alternator and the means to attach a cogged pulley for the oil pump’s HTC drive. Schwarz determined that a 23/40 pulley cog ratio would provide the proper speed for the pumps. XRP braided AN-12 lines and companion fittings take the oil to an Aviaid remote filter-mounting bracket, and then back on the supply side to a adapter fitted to the Coyote block where the OEM filter normally resides. Additionally XRP AN-12 line was used to deliver the oil from the tank to the pressure side of the pump, as well as from the pan to the pump. And finally lines were run from the cam covers to the dry sump tank, and from there to the remote Moroso breather tank.
Integrating an Oil Filter and Cooler into the System
Here’s where Setrab, the internationally renown manufacturer of fluid cooling components, takes over, with the oil going into one of their remote-mounted HyperFlow canister style removable oil filters with a fine stainless steel mesh screen. Once filtered the oil is pushed through a thermostatically-controlled valve that either routes the oil into the cooler, or sends it directly to the engine at oil temps of 185 F or below to facilitate quickly warming the oil to the proper operating temperature.
A Setrab ProLine COM cooler, which is designed for use in 600+ horsepower applications, is just under two feet wide and is nestled between T-Rex’s frame rails. The heavy-duty unit features M22 female ports, with Setrab’s ProLine hose and black/titanium finished fittings completing the circuit. The tanks, brackets and adapters are all secured with ARP polished stainless steel bolts, which are 20% stronger than Grade 8 and impervious to the elements.
Finally, the oil is transported back into the engine at the point of the OEM filter mount using XRP braided hose and fittings to a billet aluminum adapter from MMR.
Determining Oil Capacity
Finally, the engine oil, which in the case of T-Rex is Royal Purple synthetic oil, the lubricant of choice at Livernois Motorsports is added. It’s fortified with zinc and phosphorous along with Royal Purple’s proprietary Synerlec additive. The amount added? Here’s the proper way to determine optimum system capacity. Start by pouring 6-8 quarts in the tank (which in our case can hold 10 quarts), run the engine, then add oil as required so that the tank is about 2/3 full at 4,000 RPM.
The adjustable pressure regulator that’s built into the Aviaid four-stage pump, combined with the system’s excellent flow characteristics, ensures that the Coyote is well fed with a steady supply of lubricating oil. With anticipated 1+g cornering, rapid acceleration and hard braking the kind of stress put on a vehicle competing in the Optima Ultimate Street Car and autocross competition T-Rex’s dry sump lubrication system is well suited to the task.