Quote:
Originally Posted by Old Tele man
TURBOCHARGER takes its "driving" power from the waste heat-energy of the exhaust, ie: basically "free" power.
SUPERCHARGER gets its "driving" power directly from the engine crankshaft, usually via an under-driven belt ratio, ie: it's a not "free" power but rather is a "load" on the engine at all times.
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Except, a turbocharger is always creating a non-trivial amount of restriction in the exhaust, and on throttle plate controlled engines this always translates into pumping loss. Electronic wastegates can reduce this slightly though.
Furthermore, positive displacement superchargers are always equipped with bypass valves and twin screw type superchargers sometimes have electromagnetic clutches, so in most driving conditions the parasitic load is very small.
Thus, most people who add superchargers seem to report identical fuel economy, while people adding turbochargers usually see reduced fuel economy. Under full load though, a well designed turbocharger system is certainly more efficient.