Suck It Up
The primary function of a beltdriven vacuum pump is to stabilize the piston rings so there is only pressure on one side of the compression ring, as well as to reduce crankcase windage for better oil control (more power). The vacuum pump creates an atmosphere inside the crankcase ranging anywhere from 13 to 15 inches of vacuum on a wet sump (higher on dry-sump systems) and literally sucks out any blow-by inside the crankcase to promote a better ring-to-cylinder-wall seal. Conventional engines that don't utilize a vacuum pump generally have pressure on both sides of the rings, which not only hinders the ability of the rings to seal against the cylinder wall, but also poses resistance to descending pistons, robbing more power. It's important to note that while many applications can benefit from a vacuum pump, it's best suited to attempting to extract every last bit of power, and can be worth up to 20 additional ponies.