You see it all the time-the little warning that says: DO NOT OVERFILL. One place you don't see this reminder is on a high performance oil pan, but frm what I've seen it ought to be in big bold letters. I recently witnessed a simple test on a dyno where I drained one half a quart or liter of oil from a small block Chevy oil pan and not only improved the oil pressure peak rpm by as match 15 psi, but also gained an amazing 14 "free" horse power. Manufacturers specify an oil capacity in their catalogs. This number refers to the number of quarts or liter to place the oil at a given level and can be different from stock "full" mark on the dip stick. This capacity is just the oil in the pan and does not include the filter or any external cooler or filter lines. When the oil level is to high it creates a condition called windage where oil is whipped up by the spinning crankshaft, which not only cost horse power but aerates or foams the oil. It does not take much to figure out that oil mixed with air does not lubricate nearly as well as straight oil. As the foam increases at higher engine speed, the oil pressure drops. That is exactly what was witnessed on the dyno. By reducing the oil level in the oil pan, by 1/2 quart or liter, not only did the oil pressure improve by as much as 15 psi by reducing aeration, but the engine also gained as much as 14 hp. It's the classic win-win situation.

The limitation to this test is that- from a vehicle-dynamics stand point, there can be sesvere consiquences to going to far when it comes to lowering the oil level. I stopped once the oil pressure looked stable. It dropped slightly at about 6,000 rpm- but this is where I chose to end the test. One good test would be heavy breaking to ensure that the oil pressure does not plaummet when the car nose-dives. Obviously, in a road race or autocross car where high-g breaking and cornering are the norm, as slightly higher oil level maybe necessary. The best bet is to determine if the oil pressure is dropping at highter engine speed. That is an obvioius cue that the oil is aerating. Next, reduce the capacity by 1/2 quart or liter and watch the oil pressure at high rpm. If the oil pressure improves and you have no oil pressure problems under breaking, drain another 1/2 quart or liter and rerun your test. Be cautious about removing more than 1 to 1 1/2 quart or liters from the engine without careful evaluation, but this may be necessary if the engine has been severely overfilled. Smaller capacity pan don't seem to suffer the same oil- control problems. This means, only a slight improvement with small engines by reducing the oil capacity, but every case is different. The goal here is to make the engine more efficient by improving oil pressure by reducing aeration, while also potentially increasing power. When you can improve durabilitiy and increase power, that's a home run in anybody's book. END