Why a turbocharger?

The advantages from using a turbocharger are as follows:
Comparing to an engine of identical power rating in which the exhaust gases are removed in “natural” way the fuel consumption is lower and the energy of the exhaust contributes to increasing the engine’s efficiency. Due to smaller cylinder capacity the loses resulting from heat waste and friction are also smaller.

The power to weight ratio, i.e. kW (power generated)/kg (engine weight) in case of turbocharged engine is far better than in case of the uncharged one.

Turbocharged engine is of smaller size compared to the uncharged one.

The magnitude of turbocharged engine’s torque may be increased thanks to high gain of torque at low rotation speed. Full power of the engine is maintained even at the lower engine rotation. Therefore one doesn’t have to reduce gear when climbing a hill, also the vehicle more slowly loses speed.

 
The efficiency of turbocharged engine is much better at great heights. Due to lower atmospheric pressure the power loss in uncharged engine is quite substantial.

The turbocharged engines behaves quite differently – the efficiency is increase because of the difference between lower ambient pressure and higher pressure in the turbine. Therefore the lower density of air in the compressor’s inlet is compensated, hence the engine only suffers minor power loss.
Since the size of the engine is smaller also the generated noise is reduced; the turbocharger acts as an additional damper for exhaust gases.

The turbocharged engines can operate with a big air margin and this is one of the basic requirements since it allows for low emission of exhaust gases and small fuel consumption.