Twin-screw type supercharger

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Lysholm screw rotors. Note the complex shape of each rotor which must run at high speed and with close tolerances. This makes this type of supercharger quite expensive.(This unit has been blued to show close contact areas)

The twin-screw type supercharger is a positive displacement type device that operates by pulling air through a pair of meshing lobes not dissimilar to a set of worm gears. Twin-screw superchargers are also known as Lysholm superchargers (or compressors).

The intake is located at one end of the two screws, which overlap, but not completely, leaving a small pocket open. As the screws turn the pocket moves towards the exhaust side, pulling air in from the intake. The screws are machined so the pocket gets smaller, compressing the air as it moves through them. The supercharger is typically driven directly from the engine's crankshaft via a belt. Unlike the Roots type supercharger, however, the twin-screw exhibits internal compression. This increases the thermal efficiency of the supercharger beyond that of the more common Roots style supercharger.

Although the twin-screw type supercharger has more potential than the Roots type supercharger, its production costs due to close tolerances put it at a cost disadvantage. Also due to the internal compression the air exiting the supercharger exhaust "pops", this can lead to a whining, whistling or screaming noise that has to be tolerated or dealt with via noise suppression techniques.

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

Companies manufacturing twin-screw superchargers include Eaton, Lysholm, BBM, and Warner-Ishi/IHI (Ishikawajima Harima Industries).

The Ford GT, Mercedes-Benz SLR McLaren, Mazda Millenia S, and the Koenigsegg CC8S have Lysholm type superchargers.

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