Unlike a turbocharger driven by exhaust gas, a supercharger is belt-driven off the crankshaft. That means instant boost, no lag, and a linear relationship between engine RPM and boost pressure. But not all superchargers compress air the same way, and the differences matter enormously for how the engine behaves.

Roots (positive displacement, external compression): Two counter-rotating lobed rotors trap air between the lobes and the case, then dump it into the intake manifold. Compression happens in the manifold, not inside the blower. This makes Roots designs simple and cheap but thermally inefficient — they heat the charge more than they need to. The classic GM 6-71 drag racing blower is a Roots, and so is the Eaton M90 on the supercharged Pontiac Grand Prix GTP.

Twin-screw (positive displacement, internal compression): Two intermeshing helical rotors (one male, one female) progressively squeeze the air along the length of the rotors before releasing it. Because compression happens inside the unit, twin-screws are 10–15% more thermally efficient than Roots at the same boost level. Whipple and Kenne Bell use this design. The Ford GT500's 2.65L twin-screw is the OEM poster child.

Centrifugal (dynamic compressor): Essentially a belt-driven turbocharger compressor wheel. Boost builds with the square of impeller speed, so a centrifugal makes almost nothing down low and full boost only near redline. Very efficient (adiabatic efficiency 75–80%), compact, and easy to package. ProCharger and Vortech dominate this market. The old Paxton on Shelby GT350s is centrifugal.

Rule of thumb — parasitic loss: A supercharger consumes roughly 1 hp for every 2 hp it makes at the crank in gross terms (before net gain). A 400 hp gain typically costs ~200 hp to drive the blower, netting the extra power you actually feel. Twin-screws are the most efficient here; Roots the worst.

Boost curve character:

• Roots/Twin-screw: Full boost by 2,000–2,500 RPM. Torque monster off the line. Great for drag racing and street cars where response matters.
• Centrifugal: Peak boost at redline. Feels like a naturally aspirated engine that grows a second engine at 5,000 RPM. Great for road racing where you're always in the powerband.

Pulley math: Supercharger boost is set by the ratio of crank pulley to blower pulley. Smaller blower pulley = faster rotor speed = more boost. A common upgrade is a "pulley swap" — dropping from a 3.5" to a 3.0" blower pulley on a Whipple raises boost by roughly 3–4 psi, but also increases parasitic drag and heat load. Belt slip becomes the limiter above ~15 psi without an aftermarket 10-rib or cog-belt setup.