The supercharger has been around for many years, almost as long as the internal combustion engine itself.
The term supercharging technically refers to any pump that forces air into an engine - but in common usage, it refers to pumps that are driven directly by the engine as opposed to turbochargers that are driven by the pressure of the exhaust gasses. A supercharger can be powered mechanically by belt, gear, or chain-drive from the engine's crankshaft.
Superchargers draw their power directly from the crankshaft. Most are driven by an accessory belt, which wraps around a pulley that is connected to a drive gear. The drive gear, in turn, rotates the compressor gear. The rotor of the compressor can come in various designs, but its job is to draw air in, compress the air into a smaller space and discharge it into the intake manifold. To compress the air, a supercharger must spin rapidly -- more rapidly than the engine itself. Making the drive gear larger than the compressor gear causes the compressor to spin faster. Superchargers can spin at speeds as high as 50,000 to 65,000 rotations per minute (RPM).
A compressor spinning at 50,000 RPM translates to a boost of about six to nine pounds per square inch (psi). That's six to nine additional psi over the atmospheric pressure at a particular elevation (atmospheric pressure at sea level is 14.7 psi).
There are three types of superchargers:
The main difference is how they move air to the intake manifold of the engine. Roots and twin-screw superchargers use different types of meshing lobes, and a centrifugal supercharger uses an impeller, which draws air in. Although all of these designs provide a boost, they differ considerably in their efficiency. Each type of supercharger is available in different sizes, so that a match can be done to the engine attributes, such as engine displacement.
The biggest disadvantage of superchargers is that they steal power as it helps generate additional power. Because the crankshaft drives them, they must steal some of the engine's horsepower. A supercharger can consume as much as 20 percent of an engine's total power output. But because a supercharger can compress air and help increase more power, most think the trade-off is worth it.
An additional benefit is, compared to a turbocharger, is the instant response. As the supercharger is driven off the crankshaft, it will increase speed in the same rate as the engine, thereby having instant response and no lag.