Sometimes, even the torque of a diesel engine is not enough to run such big machines. To boost power, large diesels often have a device called a turbocharger attached. A turbocharger is a type of turbine – something used to move a lot of air very quickly. Jet engines also contain a turbine. In the diesel, pressure from the exhaust spins the turbocharger at a very high speed. Fresh air is then forced back into the engine. Since the engine works by pumping air, the more air you can put through it, the more power it makes. That is where the turbocharger helps. A diesel engine that has a turbocharger is called a turbodiesel. The whistling sound sometimes heard near one of these engines is caused by the turbocharger, or "turbo" for short. 