Summat to do with it being a dry sump.
This is a simple explanation of how a dry-sump oiling system works in the RSV1000 Mille, SL1000 Falco, RST1000 Futura, and Pegaso 650. This oiling system can also be found on all types of race cars (F1, Indy, circle-track, even NASCAR). This dry-sump oiling system frees up lost horsepower and prevents oil starvation problems associated with long wheelies and high G-forces. Aprilia is the only one to use this dry-sump oiling system in all of their 4-stroke motorcycles. I strongly feel that other manufacturers should also use this system.
The basic dry-sump oiling system consists of two oil pumps, an oil filter, and an oil tank.
We'll start at the oil tank, since most of you know where that is located. The oil tank always contains a minimum level of oil. The oil is drawn down the bottom hose to the first oil pump called the pressure oil pump. The pressure oil pump pushes the oil through the oil filter, and then to all major lubrication points (bearings, crankshafts, cams, transmission gears, etc.) thru oiling passages just like in all other engines. This pressure pump is analogous to the single oil pump in a wet-sump engine.
Oil splashes off the moving parts and drains to the bottom of the crankcase. Here, is the main difference between dry-sump and wet-sump. In a typical wet-sump engine, the crankcase (oil pan) is very deep and full of oil. The crankshaft partly spins through this oil causing a HP loss. The single oil pump in a wet-sump engine has its pickup somewhere in the oil pan. Under certain conditions (high G-forces, long wheelies, stoppies, etc.), this oil pickup can be sucking in air and not oil. This will starve all the moving parts for oil. NOT GOOD!!!
In a dry-sump Aprilia engine, the oil does not sit in the pan, hence the bottom of the crankcase is "dry" and very compact. A second oil pump, called the recovery or suction oil pump, returns this oil back to the oil tank through a hose. This hose connects to the top of the oil tank. With a dry-sump system the "oil pan" is effectively moved to the side of the engine (now called the oil tank). Remember, because the oil tank always has oil to feed the pressure pump, the pressure pump will never run out of oil. No oil starvation problems!!!
This system allows the engineers to make a more powerful and compact engine, and provide adequate lubrication under all conditions (high G-forces, long wheelies, stoppies, etc.). It frees up lost horsepower by not spinning the crankshaft through several inches of oil. The crankshaft is pressure lubricated not "splash" lubricated.
