Roots Type Superchargers Explained
The roots style supercharger is the oldest type of supercharger and dates back to the early 1900's when it was first used as an industrial air-moving device. In the past 30 years or so, however, the roots style supercharger has undergone drastic changes and has become so efficient and quiet that it is now commonly used as a forced induction system for automotive applications. The roots style supercharger, while still the least thermally efficient supercharger design (versus centrifugal and screw-type designs), has found a home on board top fuel dragsters as well as on modern Mercedes, Ford, and GM passenger cars as an original equipment power adder.
How it Works
The big disadvantage to the roots type supercharger is its thermal inefficiency - or its nature to produce high discharge temperatures - which robs power from the engine. With a roots type supercharger, an intercooler is almost always a necessity to bring the air charge temperatures down to an acceptable level. This poor thermal efficiency can be attributed to the fact that it has no internal compression (compression is done after the air leaves the discharge port). Additional heat is created by compressed (hot) air that leaks backwards past the rotors and heats up the temperature of the inlet charge.
The roots type supercharger is the oldest type of supercharger and still has its place in the automotive world on dragsters, smaller engines, and trucks - all of which are need power in the bottom half of the rpm range. Most major manufacturers have steered away from roots type superchargers likely because they create so much heat, even at low levels of boost. Like the screw-type supercharger, it is also difficult to create very high levels of boost with a roots type supercharger. Nonetheless, several manufacturers (Magnuson/MagnaCharger, Saleen, Allen,, Jackson - all use an Eaton roots compressor) have been able to design automotive supercharger systems that make good use of the roots type compressor's advantages while overcoming its shortcomings. If you do purchase a roots-type supercharger, expect incredible power gains right off of idle. You can also be assured that you will have one of the most simple and dependable superchargers available, which is why automobile manufacturers (GM, Ford, Mercedes) generally choose roots compressors for OE applications. An intercooler will most likely be necessary at boost levels above 6psi with a roots supercharger.