The crankshaft-driven ______ adds power by increasing the density of the air.

• A. Turbocharger
• B. Exhaust manifold
• C. Air filter
• D. Supercharger

Answer: (D)

Increasing the density of the incoming air lets more oxygen reach the cylinders, so more fuel can be burned and more power is produced. A crankshaft-driven device that does this is a supercharger, which uses a belt or gear connected to the crankshaft to spin a compressor. This compresses the intake air before it enters the engine, increasing its density and the amount of air–fuel you can burn.

The turbocharger also increases air density, but it’s powered by exhaust gas driving a turbine rather than by the crankshaft, so it’s not crankshaft-driven. An exhaust manifold doesn’t compress air; it collects exhaust. An air filter cleans air but doesn’t increase its density.