What’s the difference in actual use? Driven by a belt, chain or gears directly from the engine’s driveshaft, a supercharger represents a greater parasitic load on the engine than a turbocharger does. The increased output more than makes up for the drag, but in the overall equation, superchargers are less efficient. However, the direct connection means the supercharger’s output advantage is there even at low engine revolutions. Speaking generally, a turbo’s presence is felt only at higher rpm once the engine revs up, the exhaust gases flow and the turbine “spools up.” Conversely, superchargers are less effective at high engine rpm because they can’t keep up with the demands of a high revving engine. A supercharger geared to increase its output to meet the demand would add so much complexity and friction as to make it unfeasible. Turbos are able to keep up with the demand basically because they are driven by and driving the same medium — gas, in the form of exhaust gases and intake air: An increase in exhaust flow with rpm nets a nearly equal increase in charging pressure on the intake side.  

For what it’s worth, it seems that automakers are working to make turbos more useful at lower rpm than they’ve been conventionally, in order to even out the often lopsided power curve that is common in turbocharged four-cylinders.  

Information for this was taken from the Cars.com’s glossary, written by Joe Wiesenfelder.   

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Answered by Joe Bruzek on April 16, 2009 in Glossary | Permalink

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