Centrifugal type supercharger

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Cover of Hot Rod magazine showing Ford Flathead V8 engine with centrifugal supercharger (on top)

The centrifugal-type supercharger is practically identical in operation to a turbocharger, with the exception that instead of exhaust gases driving an impeller, there is only a compressor housing, and that is driven from the crankshaft via a belt-, gear- or chain-drive. As such the centrifugal exhibits the same benefits and down-sides. Boost increases with the square of RPM (unlike the linear nature of the positive displacement devices), however low-rpm boost suffers because air can pass back through the supercharger with little restriction until RPMs rise sufficiently to counteract the effect. Of all the belt-driven supercharger types this type exhibits the highest efficiency. The Roots type supercharger and the twin-screw type supercharger, however, produce low-rpm boost and as such feel far more reactive on the road.

Due to its design and lack of low-down boost it is often employed on near-standard compression engines. This means that it can facilitate airflow at higher engine RPMs, when most motors tend to have poor volumetric efficiency, without substantially increasing cylinder pressures at low- to mid-RPM operation, causing knock. This principle makes this type of supercharger ideally fit for a "bolt-on" type power adder, with no modification of the pistons and/or compression ratio necessary.

However, detractors of the centrifugal-type supercharger (at least in street-driven automobile applications) note that it combines the worst qualities of a turbocharger and a supercharger, since it doesn't develop appreciable boost at low RPM (Boost Threshold), but still uses up prodigious amounts of engine power to operate. When engine speed is not relatively constant, as in an aircraft engine, a centrifugal supercharger is a poor choice. Since it is crankshaft-driven and cannot benefit from a device like a wastegate on an exhaust-driven turbocharger to control its rotational speed, its boost threshold is always within a thousand or so RPM of redline. As such, the horsepower rating of the engine is greatly increased, but in a very small and nearly unusable range. The performance of the automobile will not have proportionately changed.

Many World War II piston aircraft engines such as the Rolls-Royce Merlin and the Daimler-Benz DB 605 utilized single-speed or multi-speed centrifugal superchargers. Because high-performance aircraft engines were typically mated to constant-speed propellers and did not see a great variation in engine speeds, the poor low-rpm performance of centrifugal superchargers was not an issue. Turbosupercharged engines combined a centrifugal supercharger with a turbocharger for better performance across a broad range of altitudes.

The Volkswagen G60 supercharger was invented by L.Creux circa 1905, the G in G60 standing for G-Lader (Lader being German for Charger), a supercharger whose interior resembles the letter "G". This supercharger is only mentioned here for completeness as it should not be confused with a centrifugal supercharger since it does not use centripetal force to compress air. The chambers within these superchargers reduce in size as the air heads towards the centrally located exhaust. Hence they are more like the twin-screw type supercharger in that are endowed with internal compression. They also make boost at low revolutions because of this.

The G60 engine was available in the VW Corrado but also in limited numbers in the VW Passat and the VW Golf. A similar, but smaller G40 equipped engine was available in the VW Polo during the early 1990s. The 40 and 60 denote the displacer scroll width in mm.

All supercharger types benefit from the use of an intercooler to reduce heat produced during compression.

Centrifugal type supercharger

See also