Tech Talk #24 – Panning for Power

DavidTechArticlesBy David Reher, Reher-Morrison Racing Engines

There seems to be some confusion about the true purpose of the lubrication system in a racing engine. The primary purpose of the oiling system is to lubricate the engine – period. It is emphatically *not* the place to look for horsepower in a bracket racing motor with a wet-sump oil pan.

Think of a sportsman drag racing engine as an endurance motor. It may only run at maximum power for a few seconds at a time, but those runs add up over a long season of racing. If you are a serious sportsman racer, you need an engine that can make 300 to 400 passes without looking at the bottom end. From my perspective, that’s the equivalent of running a 500-mile Winston Cup event or a 24-hour endurance race.

If you want maximum power, the best oil pan is no pan at all. A total-loss oil system is the ultimate solution for minimum windage. Many years ago we actually ran such a system on our dyno. We submerged the oil pump in a bucket of oil and fired up the engine without a pan. As you would expect, the dyno cell was a mess afterward – but we were able to see exactly how the rotating assembly threw off the oil.

I cite this experiment only as an extreme example of what it takes to make power with a wet-sump system. Obviously a total-loss oiling system is impractical on the race track; the traction and track clean-up problems would be insurmountable. The simple fact is that more power requires more pan volume – and the more room you have to spread out the oil in a wet-sump pan, the less likely you will be able to keep the oil pump pickup covered.

Unfortunately, reliability usually doesn’t sell in drag racing. That’s why some oil pan manufacturers tout the horsepower gains that are available with trick wet-sump systems. In my opinion, the places to look for power in a bracket racing engine are the cylinder heads, the camshaft and the induction system. It may sound dull, but you should look for rock-solid reliability and utter dependability in a wet-sump lubrication system – unless you are willing to inspect the bearings as frequently as the class racers who are restricted by the rulebook to wet-sump systems.

Big pans may make more power on the dyno, but the dyno doesn’t duplicate real-world operating conditions. If you think that baffles and trap doors will keep the pickup covered, I suggest that you try a simple experiment. Fill your pan with a few quarts of liquid that has roughly the same viscosity as hot oil. Tilt the pan backward at a 45-degree angle – that’s the equivalent of a 1 g launch – and watch what happens. Two g’s is about 60 degrees, and 3 g’s (a rate of acceleration that is achievable by a fast car) is around 72 degrees. You’ll see that most of the oil is standing up against the back wall of the pan instead of surrounding the oil pump pickup.

Now tilt the pan forward at the same angle to simulate what happens when the car decelerates. In fact, most cars are capable of producing more g’s on shutdown than on acceleration. Unless you have a well-defined sump, the oil pump pickup will almost surely suck air.

The damage produced by fluctuations in oil pressure is cumulative. Every time the hydrodynamic wedge of oil between the crankshaft journal and the bearing breaks down, there is metal-to-metal contact. It may last only an instant, but that is enough time to start microwelding the two surfaces. By the time you see the needle on the oil pressure gauge fall, the damage has already begun. If you tear down the engine every few weeks, this may not be cause for concern – but if you overhaul your engine only once a season, any loss of oil pressure is potentially dangerous.

Connecting rods often take the blame for oil system problems. I’m skeptical when a racer tells me that he broke a rod – nine times out of ten, the real culprit is a spun bearing caused by lack of oil pressure. If the crankshaft journal is black, the rod didn’t fail first. Broken rods don’t spin bearings – spun bearings break rods. A true rod failure will always leave the bearing intact – and it’s very rare to see that.

Sometimes good intentions produce unintended consequences. Suppose you install an oil cooler or a remote-mounted oil filter to make filter changes easier. That’s a fine idea – but now you have added several feet of line to the system that must be filled before the lubrication system is pressurized. Unless you have installed a check valve in the line, the oil will drain back into the pan when the engine is shut off. Now you’ve created the opportunity for an air lock, and you have definitely increased the time it takes for the pump to pressurize the system. If the engine loses pressure on shutdown, it will now take longer to recharge the system when you fire the engine.

I should also point out some precautions if you use a vacuum pump with a wet-sump system. We’ve tested vacuum pumps on numerous sportsman engines, and learned they are definitely worth power, especially in an engine with a tightly confined crankcase. The vacuum pump reduces the density of the air in the crankcase, which in turn reduces the resistance to the rotating assembly. It’s the same principle that allows an airplane to fly faster at 20,000 feet altitude than at sea level.

Unfortunately, too much vacuum can be a bad thing with a wet-sump pan. Remember that it is the pressure in the pan that forces oil into the pickup. When you reduce the pressure in the crankcase with a vacuum pump, you also reduce the pressure differential between the inlet side of the pump and the pan. Normal atmospheric pressure is approximately 30 inches of mercury; if you reduce the pressure in the pan to 15 inches, you have only half as much pressure pushing the oil into the pickup.

On the dyno, we see fluctuations in oil pressure when the crankcase vacuum approaches 15 inches with a wet-sump system. We use an adjustable air bleed (essentially a controlled leak) to regulate the maximum pan vacuum to between 10 and 12 inches. With the wet-sump system we install on our Super Series bracket racing big-blocks, we see no fluctuations in oil pressure at this vacuum.

In the high-tech pursuit of horsepower, racers sometimes overlook the basics. A reliable lubrication system is about as basic as it gets. All the power you gain with a marginal oiling system is useless if you’re smoking the bearings.

As a professional engine builder, I hate to see parts destroyed needlessly. I would much rather help racers step up their program to the next level than see them spend money on fixing broken motors. That is why I strongly recommend that you play it safe with the oil system and look for power elsewhere.