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Message: <blockquote data-quote="Hellion94" data-source="post: 381936" data-attributes="member: 8471">Roots style is not a category of supercharger, it's just a way of referring to them. A Roots supercharger uses 2 meshing lobes in order to compress air and force it into the engine - whereas a twin screw supercharger uses 2 screw-like objects that spin and progressively mesh together, pushing the air towards the bottom and rear of the supercharger while compressing it. Twin screws are much more efficient, and make much more power than Roots superchargers. The correct term for these types of superchargers is "Positive Displacement Superchargers." Both of these superchargers are positive displacement superchargers in that they both displace, or move, a certain volume of air with each full rotation. So when you hear the term "a 2.4L Kenne Bell" That means that the Kenne Bell supercharger in question moves (or displaces) 2.4L worth of air volume per rotation, and the same holds true for roots superchargers, however they are commonly referred to using a system of sizing developed by GM when it first started including roots style superchargers on their cars a very long time ago. The term is 4:71, or 6:71, 8:71, 10:71, 12:71, and 14:71. This originally referred to the amount of cylinders and cu. in. size of the engine that the particular supercharger was designed to go on. So a 6:71 would be designed to go on a 6 cylinder engine that displaced 71 cu. in. This term is now just a common way of classifying supercharger sizing, and has nothing to do with what size engine the superchargers are meant for.</blockquote>