What is a turbocharger?
A turbocharger, or turbo, is an air pump that drives additional air into the combustion chamber mixing with the injected fuel to increase air and fuel into the engine - which in turn increases the amount of power the engine is able to generate.
How does a turbocharger work?
In essence, a turbocharger is an air compressor and a turbine bolted together. The 'hot' side consists of a housing containing a turbine wheel, through which the engine's exhaust gases are passed. The 'cold' side contains the compressor wheel, an air inlet and a discharge port.
When the engine is running, its exhaust gases drive the turbine, which causes the compressor to spin. This compresses the air that's being drawn in, then this high-pressure air - at a 'boost' pressure, above atmospheric - is sent to the engine.
Most conventional turbochargers also have an internal wastegate. This is a pressure-activated valve which controls the maximum boost level. As the turbocharger speeds up, producing more boost, excess pressure causes the wastegate to open - causing exhaust gas to bypass the turbine, slowing it down. Without this, the turbocharger would simply keep accelerating, eventually causing damage to itself and the engine.
Being driven by the engine's exhaust gases is also what primarily differentiates turbochargers from superchargers; a supercharger is a compressor that's typically driven directly by the engine, through a belt or a gear drive.
History of the turbocharger
BMW and Porsche were also producing turbocharged cars.
Nowadays, many manufacturers combine small, economical engines with turbochargers. These 'downsized' engines are designed to match bigger engines on the performance front, while also reputedly offering improved efficiency.