Modern Cars and Turbocharging – The Basics

Driven by the need for more fuel efficiency and while at the same time needing more horsepower to move heavier cars, there are few manufacturers nowadays who don’t use turbocharging, or supercharging, as a means to increase horsepower, increase fuel efficiency and improve fuel emissions. Both types of forced induction (turbochargers and superchargers) have their own strengths and weaknesses, although turbos seem to have prevailed lately with manufacturers. Both turbos and superchargers are basically air pumps, which compress air which is literally forced into the engine, as opposed to air that is drawn by engine vacuum in normally aspirated engines. Fuel is introduced into the engine by the ECU via the fuel injectors, based on the input from various sensors so that optimum engine combustion is achieved.

A supercharger bolts on to an engine and is driven off the crankshaft pulley. This is the reason many people dislike superchargers. Because it is directly connected to the engine, the supercharger introduces a parasitic load that increases the more boost it produces. Then there is also the characteristic supercharger whine that is music to some but obtrusive for others. But the supercharger is favored by many hotrodders because it has near-instant response when called upon to produce boost.

In contrast, turbocharging connects to an engine’s exhaust manifold. Shaped like a snail, a turbocharger has both a turbine wheel and a compressor wheel. Both are connected to each other by a shaft that is lubricated with engine oil. The turbine wheel is what is driven by the exhaust gases and the compressor section is what forces air into the engine. Because the turbine wheel is driven by the exhaust, there is no parasitic load as in the case with superchargers. While many proponents claim that turbochargers produce free horsepower since they are driven off the exhaust, this is not exactly the case. Because of their placement, turbocharging introduces back pressure in the exhaust. But this back pressure is small and cannot be compared to the parasitic load a supercharger imposes on an engine. Meanwhile, the turbo’s compressor section sucks in air and compresses it to be fed into the engine.

When you compress the air going into the engine, more fuel can be added. Therefore, you increase the engine’s efficiency over that of an engine which only draws air through vacuum. This is why increases in orders of magnitude are not uncommon with turbocharging (or supercharging, for that matter). Automobile manufacturers have taken advantage of this by building smaller engines and then using turbochargers on them. Smaller engines have obvious advantages in fuel efficiency and exhaust emissions. Through the use of turbocharging, manufacturers have achieved the seemingly opposed goals of more power and less fuel consumption.

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