A dry-sump system is a method to manage the lubricating motor oil in four-stroke and large two-stroke piston driven internal combustion engines. The dry-sump system uses two or more oil pumps and a separate oil reservoir, as opposed to a conventional wet-sump system, which uses only the main sump (U.S.: oil pan) below the engine and a single pump. A dry-sump engine requires a pressure relief valve to regulate negative pressure inside the engine, so internal seals are not inverted. Dry-sumps are common on larger diesel engines such as those used in ships, as well as gasoline engines used in racing cars, aerobatic aircraft, high-performance personal watercraft and motorcycles. Dry sump lubrication may be chosen for these applications due to increased reliability, oil capacity, reduction of oil starvation under high g-loads and/or other technical or performance reasons. Dry sump systems may not be suitable for all applications due to increased cost, complexity, and/or bulk, among other factors. Design Engines are both lubricated and cooled by oil that circulates throughout the engine, feeding various bearings and other moving parts and then draining, via gravity, into the sump at the base of the engine. In the wet-sump system of most production automobile engines, the oil that's not actively circulating is stored in the sump, which is large enough for this purpose. A pump collects oil from the sump and directly circulates it back through the engine. In a dry-sump system, the oil still falls to the base of the engine, but into a much shallower sump, where one or more scavenge pumps draw it away and transfer it to a (usually external) reservoir, where it is both cooled and de-aerated before being recirculated through the engine by a pressure pump. The sump in a dry-sump system is not actually dry; it is still wet from oil draining from the engine. The reservoir is usually tall and narrow and specially designed with internal baffles, and an oil outlet (supply) at the very bottom for uninhibited oil supply even during sloshing. A dry-sump system requires at least two pumps - one pressure and one scavenge - and sometimes as many as four or five scavenge pumps are used to minimize the amount of oil in the engine. Dry-sump designs frequently mount the pressure pump and scavenge pumps on a common crankshaft, so that one pulley at the front of the system can run as