Turbocharger is one of the two most commonly used compressors in automobiles (other one being Supercharger). As the name suggests, a compressor is a device that compresses air. In case of a turbocharger, it compresses the air coming out of the exhaust stroke of a 4-stroke engine. It is located between the intake manifold and the exhaust system. The inlet of a turbocharger compressor is located at the exhaust and the outlet at the intake.
There is a valve at the junction of the compressor inlet and exhaust which opens only when enough pressure is built up by the air breath by the engine. If the amount of air is not sufficient to open the valve, the air will bypass the turbocharger and the gases will be emitted as in normal vehicles. However, once the amount of air, or rather the pressure of the air present is enough to open the valve, the exhaust gases enter the turbocharger, and that, as a result turns the turbine in the turbocharger which compresses the air to make it denser and emits the compressed air into the intake manifold, resulting in a higher air: fuel ratio, which results in better performance. The time required to build up enough pressure to open the valve can be termed as “Turbo Lag”. Every turbocharger has its own capacity to handle the amount of pressure of air that enters and exits the turbocharger, and once that limit is reached, the excess air is bypassed directly through the exhaust pipe.
The capacity of a turbocharger depends on its size. The size of the turbocharger can be determined based on the type of purpose it is going to solve. If the boost is required at lower engine speeds, a smaller sized turbocharger does the job, while if one needs the boost at higher engine speeds, a bigger turbocharger is used.