What’s the Difference between Turbos and Superchargers

From 3arf

The main difference between a turbocharger and a supercharger, is in the method of driving the unit. A turbocharger has a turbine wheel on one end of a ball bearing supported shaft, on the opposite end of the turbine shaft is a centrifugal compressor impeller. Attached to the exhaust system of the engine, it uses the hot exhaust gases normally leftover from combustion, to cause the turbine wheel to rotate at very high speed. The rotation of the compressor impeller at the opposite end produces both airflow and pressure. The resulting pressure is then fed into the intake manifold increasing the engines efficiency from around 80%, to 100% or above.

A supercharger is a compressor that can be driven by either belts, chains, or gears, from the crankshaft of the engine. It can be one of several styles of compressor. They may be of the centrifugal type, like the turbocharger. In which case an internal gearbox is part of the unit, to raise the rpm to the level required for a centrifugal style impeller, as much as 60-80,000 rpm. This style of compressors' airflow increases with an increase in rpm. Centrifugal superchargers are found mostly onrace carsand some exotic sports cars.

More likely to be found on a factory equipped supercharged car is the positive displacement or "Roots" type supercharger. The Roots style is called positive displacement, because it pumps the same amount of air per revolution regardless of engine rpm. This is the type that has been used on large semi trucks for many years. Due to the much lower operating rpm range of this style of compressor, much less maintenance is required on the Roots supercharger. Because the Roots compressor operates at roughly engine speed, it generally must be physically larger in order to generate the same airflow as the centrifugal style.

The supercharger draws power away from the engine due to the belt drive required for rotation. While the turbo uses what is normally a waste product of the engine, basically free horsepower. As a result of this difference, the supercharger will never approach the turbo as far as efficiency is concerned. Superchargers especially the Roots type, are notorious for heating the air being fed to the engine further reducing efficiency.  Turbochargers also increase fuel economy, by allowing auto makers to install a smaller cubic inch engine than would normally be required. A properly sized turbo or supercharger can easilydouble the engine output.

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