Turbos and turbocharging have become buzzwords of the present-day motoring scene. It is not a new idea, though. The turbocharger - short for turbine-driven supercharger - dates back to 1905. By the 1920s turbochargers began to appear on diesel locomotives and marine engines, and by the time of the World War 2 they were in use on military aircraft. After the war various manufacturers actively developed turbo-diesel engines for heavy trucks, and in due course such engines achieved total dominance in this segment. On petrol-engined passenger cars, turbos have had a somewhat patchy, on-off history, but in racing and rallying, on the other hand, turbocharged engines had unqualified success.
In the current field of passenger cars, turbocharging has gained almost universal acceptance on diesel engines, even small diesels, while it is also becoming increasingly popular on petrol engines.
A turbocharger, distilled to its basics, consists of two bladed wheels, fixed at the ends of a common shaft. At the one end, inside its housing, sits the turbine wheel. At the other end, in a separate housing, is the compressor impeller wheel. Between them, sealed off from both housings, is the bearing assembly on which the shaft rotates. The spinning compressor impeller draws in air from outside, then uses centrifugal effect to push the air under pressure into the inlet manifold. The net effect is that air enters the cylinders under higher than atmospheric pressure, resulting in an increased mass of air packed into each cylinder during the inlet stroke.