Pardon the pun, but oil pan technology is a slippery subject. It’s often both ignored by one camp and overvalued by another. There’s no black magic here. No matter what you are running, a racing oil pan serves only two purposes: collect oil around the pickups so it is always available to the engine and keep the viscous liquid cool and away from the spinning crank to save power.
Sounds simple, but add in all the other variables that come with circle-track racing and everything changes. Many stock classes require stock-style pumps that rob volume from the pan and make it difficult to ensure the engine is never starved of oil. Engine and chassis builders demand the engine be as low as possible, severely limiting oil-pan depth and volume. Finally, how do you get prime performance in claimer classes where funds are restricted?
Wet vs. Dry
There are two major divisions in engine oiling systems: wet and dry sump. “Sump” simply means the chamber in the bottom of any engine that collects lubricants for redistribution. In a piston engine the oil pan is the sump. A wet-sump system is the same used in passenger cars and mostly seen in the lower levels of racing. Wet sump means engine oil is collected and stored in the oil pan until it is recirculated by the oil pump back through the engine. In a dry-sump system oil is collected in the oil pan and immediately sucked, or “scavenged,” to an external tank before being recirculated to the engine. Because the sump is not used to store oil, it is referred to as “dry.”
A dry-sump system has several advantages over wet, but the main one is additional power. Because there is only a minimum of oil in the pan, windage—oil clinging to or splashing against the rotating assemblies of the engine—is greatly reduced. In addition to evacuating oil from the pan, the external oil pump creates a vacuum inside the pan and block that further increases horsepower by improving ring seal. Other advantages of a dry-sump system are increased oil capacity because of the external tank, the ability to easily add remote oil coolers, and because the pan doesn’t store oil, it can be quite shallow to allow for lower engine placement.
Scrapers, Screens and Louvers
The biggest enemy to power inside the oil pan is windage. Unless it’s in the bearings, any time engine oil comes in contact with the crank and connecting rods it robs power. “The main purpose of what we try to do in an oil pan is get the oil away from the crankshaft,” says Ricky Schroder of C-Line Engineering. “It doesn’t just have to be the ends of the crank splashing in the oil. Even when it’s on the crank oil acts like a rope, it wraps around it. So you want the crank free of oil so it spins more freely.”
Scrapers are the first line of defense when it comes to removing oil from the crank. A scraper is simply a strip of sheetmetal attached on the right side of the block between the block and oil pan. It extends close to the crank and is designed to knock off drops of oil as the journals and counter-weights of the crank spin past.
A windage tray is designed to keep oil from splashing up from the bottom of the pan and back onto the crank—a condition that happens all too often in the rough conditions in racing. A good windage tray extends across the width and length (if there is not an internal oil pump) of the pan. Traditionally, windage trays have been a directional diamond screen, but more and more manufacturers are offering a louvered windage tray.
“We believe louvered trays are probably the way to go in the future,” explains Jack Teixeira, technical sales for Moroso Performance Products. “If you put a radius on a diamond screen to make a windage tray, you are reducing the area of each diamond-shaped hole. You are making a smaller hole that the oil has to go through. We did many dyno pulls and found this louvered-tray design that reduced the oil temperature by 60 degrees over diamond screen. The oil wasn’t beating on the screen; it was getting the oil back to the sump area and giving it time to cool off.”
Power Pouches and Kickouts
Because they have the dual role of collecting and storing oil, racing pans for wet-sump systems tend to be much more complicated than their dry-sump brothers. Power pouches increase the area on the right side of the pan. The centrifugal force of the spinning crank wants to throw oil off with significant force at an angle. If the sidewall of the oil pan is too close, the oil simply hits the wall and bounces back onto the crank. Schroder says C-Line feels, based on dyno tests, that 2.5 inches of extra space in the kickout is plenty, any more and the pan can be difficult to fit with other chassis and engine components.
Kickouts look much the same but serve a different purpose. To solve the problem of increasing capacity despite limited available depth, oil-pan designers have instead gone wider by building “wings” into the bottom of the pans. This allows greater oil volume in the pan without raising the oil level closer to the windage.
“Having a kickout is always a plus on a wet-sump pan,” Teixeira says. “You should always have one if your sanctioning body allows it. A kickout increases your oil capacity, and it really doesn’t hurt you weightwise because the extra oil is down low in the car.”
Dams and Gates
Oil control is vital under racing conditions. Even in slower classes, race cars will experience greater g-forces regularly—both under acceleration, deceleration and laterally—than a passenger car will probably only see in a wreck. It only takes a second for an oil-starved engine to self-destruct, so the greatest job a wet-sump oil pan must perform—more important than keeping oil away from the crankshaft or keeping the oil cool—is to always have oil available at the oil-pump pickup.
In racing pans this is done with a system of gated oil dams inside the pan. Dams are placed to concentrate the oil around the pickup and hold it there even when centrifugal forces or sloshing wants to push the oil away. Gates are one-way trap doors that allow oil to pass through a dam in one direction but not another. When purchasing a pan for your car, be sure the manufacturer knows the type of track you will be racing on. When your car is at speed, the oil is always going to be concentrated to the right, but depending on the banking and size of the track, caution and pace laps can require an adjustment in the configuration of oil dams.
Construction and Capacity When it comes to oil capacity in a wet-sump pan, more is almost always better. Since the oil is contained low in the car, the extra weight is not a big consideration, but the volume helps the oil resist overheating and dilutes contamination. Most high-end wet-sump pans have a seven-quart capacity, not including the oil filter. This is not as big a consideration in a dry-sump system since a separate container is used to store the oil, and the pan’s only job is to collect the oil before being scavenged by the oil pump.
“I’m not really worried about weight as much as the volume of oil,” adds Teixeira. “We are weight conscious, but for the Saturday-night racer you really need to go for durability and reliability. If you are weight-conscious and run too little oil, then you are really exposing yourself. If something happens—the oil is not in the pickup area where it needs to be because you don’t have enough in the system and most of it is hanging out in the heads and stuff—then we have a bigger problem than weight—you’re broke.”
Construction is almost as straightforward. Pans either begin life as a stock core that is heavily modified or as virgin sheets of aluminum. Either way, the prime considerations are a clean, consistent weld, and the top is level to provide a good seal when it is mounted to the block.
“Most of the top pans are created on a fixture,” explains Ken Sink of Milodon. “You should be able to lay a pan upside down on a flat surface and see that all the pan rails are square and not taco-shaped. If the oil pan isn’t flat to start with, you will have to pull them down with the bolts, and then it will always leak or put a crimp in the rear seal or something. You can’t have a leaky race motor, so make sure the pan rails are level to start with.”
