 |  | | | Not all superchargers are alike, and each type requires a different installation procedure. For those not familiar with the technology, a supercharger is essentially a pump that forces more air into an engine, allowing it to burn more fuel and make more power. Bolting on a blower gives you the most bang-for-the-buck of any engine upgrade on the aftermarket. Superchargers come in three basic varieties: centrifugal, Roots, and twin-screw.
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A centrifugal blower is basically a turbocharger that's driven by a belt or gear system, rather than the engine exhaust. The Roots and twin-screw types are positive-displacement superchargers that produce the same level of boost at any rpm, from 2000 rpm and up. The twin-screw differs from the Roots, though, in that it compresses the air between two intermeshing rotors, usually differentiated as male and female. In contrast, the rotors on a Roots type are "asexual," in that they have identical shapes, and they push air on their outer surfaces, which flows along the inner sides of the case. Due to these differences in configuration, the Roots type usually has a much larger housing than the twin-screw setup.
While Roots blowers have proven themselves in a wide variety of applications, from WWII aircraft to truck diesels to hot rods, the twin-screw has several advantages. In addition to being generally more compact, it requires less power to drive it and runs cooler, and since it compresses the air, it provides more boost as well. In addition, even though a twin-screw supercharger may not necessarily provide a higher peak horsepower than a centrifugal blower (depending on the setup), it does provide more boost and thus power throughout the midrange of an engine's powerband.
That midrange torque is a real benefit on a large SUV, such as on a Ford Expedition's 5.4-liter V-8 (shown in the following sequence of photos). You can expect an increase in power of 40 percent or more, depending on the pulley size installed. The smaller the pulley, the faster the supercharger spins, and the more boost it generates. Another advantage of a twin-screw is that the pulley's sizes can be replaced in a matter of minutes to produce various levels of power. That way, you can enjoy a relatively mild increase in power for daily driving, and then dial up the boost on the weekend for some high-performance driving or heavy-duty hauling.
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Kenne Bell, 10743 Bell Court, Rancho Cucamonga, CA 91730, 909/941-6646, www.kennebell.net
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