Like turbochargers, a supercharger is a device that also forces more air into the engine. However, unlike turbos, a supercharger is powered by a belt that is directly connected the crankshaft. Because of this, they are generally more responsive and do not suffer “lag” as badly as turbocharged cars do. On the flip side, since they are driven directly by the engine, they tend to sap power from the very engine it’s supposed to boost. But since they generate more power than they use, the trade-off is considered worthwhile. An intercooler is also used in supercharger setups to further increase the density of air and improve its overall effectiveness.
There are three main types of superchargers: roots, twin-screw and centrifugal. Roots and twin-screw types of superchargers use meshing lobes to compress air, while a centrifugal supercharger uses an impeller, which sucks in air.
Roots supercharger are very old in design and have been in existence since the early 1900s. It consists typically of rotors with three or four lobes that, when in rotation, trap air in surrounding pockets around the lobes and move them to the intake tract of the engine. For this reason, they are often referred to as blowers.
Twin-screw superchargers are somewhat similar in design but use meshing lobes that resemble worm gears to compress air in the housing. They are more efficient than Roots superchargers and provide very good response because boost is produced almost instantaneously at very low engine speeds. However, twin-screw superchargers usually cost more too as they need to be built with close tolerances and high precision to ensure operating efficiency.
Finally, a centrifugal supercharger uses impellers to draw more air into its compressor housing, which is not that different from a turbocharger, except that it is driven by the belt instead of exhaust gases. Because of this, centrifugal superchargers are more effective and will produce more boost as engine speeds increase. On the flip side, they are less efficient and unresponsive at low engine speeds.