A turbocharger acts in a similar way as a supercharger and pressurises the air at the inlet manifold. As the inlet valve in the cylinder opens, a greater mass of air is drawn into the cylinder to be burnt with the fuel. More power is generated at each engine speed. 

Unlike the supercharger it does not feed off the power output of the engine. The turbocharger uses the waste energy from the exhaust gas to drive a turbine wheel that is linked to the compressor through a shaft. At high altitudes, there is insufficient oxygen to burn the fuel, resulting in low power and black smoke. 

At high altitudes the turbocharger rotates faster to increase delivery of air to the engine to compensate. So a turbocharger maintains power from the engine and produces clean emissions. 

Fitting a turbocharger and an air cooler can increase engine power even more. An Intercooler removes the heat of compression between the stages of a compressor whereas an aftercooler reduces the temperature of the air leaving the compressor. Delivering cold air means that there is more oxygen per cylinder (cold air has a higher density than warm air) thus more engine power.

To conclude, the benefits of turbocharging are: 

• increased engine power output (in the region of 50% increase)
• improved fuel consumption (improved pressure balance across the engine)
• improved emissions
• altitude compensation