A common, but perhaps more correct, term for a Roots supercharger is "blower. One defining characteristic of a Roots is that charge air compression occurs outside the supercharger, in the space between it and the intake valves. In effect, it blows air into the intake manifold where it becomes compressed due to the system's pushing more air in than can flow out.

The Roots blower was patented in 1860 by two brothers, Philander and Francis Roots, as a ventilating device for blast furnaces, grain elevators and coal mines. In the last half of the 19th century they were quite common in those applications and that ancestry is key to understanding that a Roots is a device which moves air rather than compresses it.

Later, the Roots idea transferred to the street high-performance aftermarket and the Eaton Corporation developed a small, compact Roots blower for original equipment use on some performance cars, luxury sedans and, yes, pick-up trucks. Buick, Pontiac, Ford, Lincoln, Jaguar and Mercedes Benz are just a few brands using the Eaton blower, the design of which is now in its fifth-generation.

Let's take a closer look at some features of the Magnuson Radix Supercharger as used on the THR Silverados. The word "Radix" is Latin for "root" or "origin," an appropriate name, indeed. Radix are based upon Eaton, fifth-generation, M112 superchargers but they're not simply "rebadged" Eatons. Magnuson uses many of Eaton's  internal pieces but manufactures its own supercharger case, intake manifold, charge air cooler and drive system.

What actually moves the air through a Roots blower is a pair of contrarotating, tri-lobe rotors which mesh as they turn. The tighter the fit of the lobes, the more efficient the blower is, however, there must be some clearance or the rotors won't turn. If the clearance is too great, the supercharger is inefficient because of leakage past the lobe edges. If the clearance is too tight, there is a high level of resistance to rotation. To both tighten rotor clearance and reduce friction, one trick Eaton began using with its fifth-generation Roots is to coat each rotor with an abradable powder coating or (APC). During the break-in period, in the first few hundred miles of operation, a small portion of this coating abrades away, leaving the contact areas at the tips of the rotor lobes perfectly matched to each other and able to run extremely close.

This is Magnuson's Radix case. At top left, just inside the blower inlet is the bypass valve butter fly. At lower right, on the side of the blower case if the vacuum motor that operates the valve. Image: Magnuson Products.

Eaton rotors are twisted 60 degrees. Helical rotors, along with specially designed inlet and outlet port geometry in the blower case, help to reduce pressure variations resulting in a smooth discharge of air and a lower level of noise during operation. This arrangement, also,  improves efficiency. With helical rotors, the supercharger can run at up to 14,000 rpm, making for a small blower for a given boost and air flow output. The Eaton's axial intake further reduces package size.

Another "secret of the Radix" its bypass valve. This small valve, between the the throttle body and the intake manifold, increases fuel economy and reduces parasitic power loss. The bypass is operated by a vacuum actuator and is normally closed. When manifold pressure is low (high vacuum typical of light throttle operation) the actuator opens  the valve, allowing charge air to flow from the throttle body directly into the intake manifold, bypassing the blower and equalizing pressure in the system. The bypass valve open at low manifold pressure eliminates parasitic loss in a practical sense. Magnuson superchargers running with an open bypass consume only about one horsepower. When the supercharger begins to make boost, the bypass valve snaps closed, allowing pressure to build in the intake ports.

All Radix used in THR applications have a "charge air cooler" which some call an intercooler. During compression, charge air temperature rises. Because a temperature increase reduces air density, negating some of the effect of compression, and makes the engine more prone to detonation; there is an advantage in cooling the air after it exits the blower but before it goes into the cylinders. The Radix charge air cooler is built into the intake manifold.

Lastly, Radix systems used on THR Supercharged Silverados are approved by the California Air Resources Board. The CARB "E.O. number" makes them street-legal in all 50 states, including California with its stringent "Smog Check" program.