Those gumball tires and suspension mods now make your track-day, Pro Touring Camaro grip like a Trans-Am car. But in the middle of a long, high-g corner the oil-pressure warning light suddenly emits a bright-red glow and the gauge sits at zero. You immediately lift off the throttle and hope this has not scored the bearings. It’s a sickening feeling.
To combat this starvation situation, on race tracks, many racers are employing a dry-sump oil system. But we wondered if a dry-sump system is viable or necessary in a street car, and asked the folks at Moroso Performance Products for some input. Moroso has been continuously improving engine oiling for years, and we knew we could get the right answers.
The hard line between race cars and street cars is blurring. Drag Week puts six-second cars on the highway, and track-day events now tout machines that are increasingly closer to road race cars rather than mere street cruisers. This performance escalation is creating a gray area between race car and street car as more pure-race components find their way to the street. That even extends to dry-sump oiling systems. This creates the question: “does a dry sump have a place on a street car?” The answer is as complex as the question is simple.
The Good And Bad
Perhaps a simple answer would be yes, if your street car runs quicker than 8 seconds in the quarter-mile or can negotiate corners so well it is constantly subjected to lateral loads in excess of 1-g-plus. These are areas where a dry-sump excels and can offer significant advantages for engine life – and perhaps even a small horsepower advantage. But, like other highly prized things in life, dry-sump systems don’t come cheap.
“Dry-sump oil systems are a big commitment from an expense standpoint,” said Thor Schroeder, marketing manager at Moroso. “A three-stage setup can cost several thousand dollars, and as ‘stages’ are added, so do the costs. The end result is, you get what you pay for. In other words, dry-sump oiling systems are the safest, most dependable oiling systems available.”
Dry-sump oiling systems have a place in the performance world, and as street cars continually push the limits of performance, race car solutions are almost a necessity. An excellent example of this is when GM blessed the LS7 engine in the 2006 ZO6 Corvette with a factory dry sump. These cars produce such excellent lateral-g stickiness, GM felt it had to include a dry-sump system.
With Pro Touring cars now capable of generating lateral-g numbers well into the 1.2-g zone, this places an enormous strain on a wet-sump oiling system to ensure the pick up is constantly submerged. To hammer this home, if you place a glass quart-container half-full of water in your car in a secure place and apply a 1g lateral force to that water, it will be forced sideways against one side of the jar at a 45-degree angle. If the oil-pump pick up happens to be located in that area where the water has migrated away, the oil pressure will instantly drop to zero. You don’t need us to tell you this is a condition that should be avoided.
Can a wet sump work as well as dry-sump system? “Yes and No,” Schroeder stated. “I know that sounds confusing, but let me explain. Even though Moroso sells three different series’ of dry-sump pumps, production and custom dry-sump oil pans, and production and custom dry-sump tanks, certain applications are better suited to a wet-sump system than a dry-sump system. On street applications, all but the most exotic and high-performance street cars are better suited to a wet-sump system. This is because a dry-sump system adds complexity, cost, a user that has to be more mindful of what the system is doing, and more maintenance.”
A Dry Way To Keep Things Oiled
As its name implies, a dry-sump system relocates oil storage from the pan into a vertical, external reservoir. This ensures the inlet to the pump has a constant supply of oil. While the idea is simple, its execution is a bit more complicated. This is because the dry-sump pump is now externally located – usually belt driven by the crankshaft. At a bare minimum, a dry-sump system employs two circuits – one for scavenge, and the second for pressure. A typical dry-sump system will use two to three scavenge points to pull oil out of the engine. More exotic systems will use as many as five scavenge points in the oil pan, lifter valley, and sometimes even the valve covers.
You can think of a dry-sump pump like a loaf of bread that has been sliced into sections. Each section contains a set of gears that operate either as a scavenge or a pressure side. “A dry-sump oiling system consists of the dry-sump pump itself – which can have one through six stages,” Schroeder said. “The stage designation refers to how many scavenge and pressure sections the pump has. A four-stage oiling system would have three oil pump pick-ups in the oil pan itself. Each one of these pick-ups would be plumbed to the three scavenge sections of the oil pump.”
So, a four-stage pump would be three stages of scavenge matched with a single pressure-stage. Regardless of the number of scavenge stages, there is always only one pressure stage.
Most normally aspirated engines can run quite efficiently with a three-stage package. More scavenge sections can be added, but this adds complexity and cost that generally delivers only a very minor improvement in performance.
One additional advantage of a dry sump is the multiple scavenge points can generate a vacuum in the engine’s crankcase. By drastically reducing pressure inside the crankcase, this increases horsepower by reducing the work required by the back side of the pistons to push the air around. Enhanced oil scavenging also minimizes the volume of oil swinging around inside the crankcase, which also improves power. These gains are generally small – perhaps 10- to 15-horsepower – depending upon the engine’s size and RPM achieved, but the increased power does indicate efficiency improvements.
In order to create this vacuum, the engine needs to be sealed. The amount of vacuum pulled from within the engine can be determined in several ways. Most dry sumps are designed to run at 50-percent of crankshaft speed or slower. Changing the pump speed has a direct effect on the amount of vacuum the pump will create. Another way to regulate the vacuum level is with a vacuum relief valve. For example, Moroso sells a valve that offers a 10-inch Hg range of adjustment (between 10- and 20-inches Hg). For a street engine, keeping the vacuum level below 10 inches is probably a good idea.
Schroeder added, “Since proper dry-sump pumps create vacuum, to gain the most horsepower, a ring package that takes this into consideration needs to be in the mix. We have seen on our in-house dyno – and gotten feedback from our customer’s that have experienced a 10 to 15-percent increase in horsepower when going to a properly set up dry-sump system.”
Another advantage of having an external oil pump and drive is that pump speed can be custom set to a desired pressure. Since dry-sump pumps are designed to run at 50-percent or less of crankshaft speed, for a 7,000-rpm engine, this would put the pump speed at 3,500 rpm or less. The volume of oil the engine demands is one part of the equation, along with the potential for pulling vacuum to improve power. On most systems, peak oil pressure can be quickly fine-tuned using an external bypass setting.
The reason for the external, vertical tank is to create a very stable source for oil to enter into the suction side of the pressure pump. But the tank offers an important secondary function that is less appreciated. These tanks are not simple containers, but instead, feature a complex maze of steps, channels, and screens intended to separate air from the oil. Inside any high-RPM engine, oil tends to foam. If immediately introduced back into the oil pump, this will reduce oil pressure as the air is compressed. According to John Schwartz, president of Aviaid Performance Oiling Systems, just the pressure created by the weight of oil in the vertical sump will help push air out of the oil, producing a more-consistent volume of oil to the engine.
One of the more challenging aspects of using a dry sump for the street is finding a suitable location for the tank. These tanks are always vertical, and are offered in diameters ranging between 6, 7, and 9 inches. They also vary in height for capacities from five quarts all the way up to five gallons. Beyond finding a decent spot for this reservoir, there’s also the challenge of mounting the pump drive and routing the considerable lengths of -12 AN hose.
Assuming this engine will be used in competitions such as track days or extended autocross situations, an oil cooler is also a consideration. In this case, the cooler is most often placed on the pressure side, with the filter located between the pump and the cooler.
Is The Cost Worth The Benefit
As you can imagine, a dry-sump system is an expensive investment. A basic three-stage system for a small-block Chevy with a pump, mount, oil pan, three-gallon oil tank, and remote filter and mount will run in the mid-$2,000 range. That does not include the investment of roughly $600 or so for -AN lines and fittings. These prices are based on an inexpensive base system – more expansive dry-sump systems can be much costlier.
Dry-sump lubrication systems have always been aimed at race-bred applications, but as street cars continue to push the envelope in terms of lateral-g handling, and small-tire drag cars run in the 8-second zone, you will probably start to see more street cars with dry-sump systems.