A supercharger is an air compressor that helps an engine make more power by pushing extra air into the cylinders. More air means the engine can burn more fuel each cycle, which increases the force on the pistons. This is called forced induction because the intake air is driven in under pressure instead of entering only by atmospheric pressure.
Superchargers matter because they can increase horsepower without making the engine much larger.
Key Facts
- Power increases when more air and fuel burn in each cylinder per cycle.
- A supercharger is driven by the engine, usually through a belt, chain, or gears connected to the crankshaft.
- Boost pressure is the pressure above atmospheric pressure in the intake manifold.
- Absolute intake pressure = atmospheric pressure + boost pressure.
- Engine air flow roughly increases in proportion to absolute intake pressure if temperature and efficiency are similar.
- Power used by the supercharger comes from the engine, so net power gain = added engine power minus compressor drive power.
Vocabulary
- Supercharger
- A mechanical compressor that forces extra air into an engine intake so the engine can burn more fuel and produce more power.
- Boost pressure
- The extra pressure above normal atmospheric pressure that a supercharger creates in the intake system.
- Intake manifold
- The set of passages that distributes incoming air, or air and fuel mixture, to the engine cylinders.
- Crankshaft
- The rotating engine shaft that converts piston motion into rotational motion and can also drive a supercharger.
- Intercooler
- A heat exchanger that cools compressed intake air to make it denser and reduce engine knock risk.
Common Mistakes to Avoid
- Assuming a supercharger makes free power is wrong because the compressor takes mechanical power from the crankshaft to spin.
- Confusing a supercharger with a turbocharger is wrong because a supercharger is mechanically driven by the engine, while a turbocharger is driven by exhaust gas energy.
- Ignoring air temperature is wrong because compressing air heats it, and hot air is less dense than cool air at the same pressure.
- Adding boost without adding fuel is wrong because the engine needs the correct air fuel ratio to burn safely and make power.
Practice Questions
- 1 An engine has an intake pressure of 14.7 psi at atmospheric pressure. A supercharger adds 7.0 psi of boost. What is the absolute intake pressure in psi?
- 2 A naturally aspirated engine produces 200 hp. If supercharging increases the engine's gross power by 70 hp but the supercharger takes 15 hp to drive, what is the net horsepower?
- 3 Explain why an intercooler can help a supercharged engine make more power even though the supercharger has already compressed the air.