Blower Design Views
It is named for the brothers Philander and Francis Marion Roots of Connersville, Indiana, who first patented the basic design in 1860 as an air pump for use in blast furnaces and other industrial applications. In 1900, Gottlieb Daimler included a Roots-style supercharger in a patented engine design, making the Roots-type supercharger the oldest of the various designs now available. Roots blowers are commonly referred to as air blowers or pd blowers.[1]
The Roots design was commonly used on two-stroke diesel engines (popularized by the Detroit Diesel division of General Motors), which require some form of forced induction, as there is no separate intake stroke. The Rootes Co. two-stroke diesel engine, used in Commer and Karrier vehicles, had a Roots-type blower but the two names are not connected.
The superchargers used on top fuel engines, funny cars, and other dragsters, as well as hot rods, are in fact derivatives of General Motors Coach Division blowers for their industrial diesel engines, which were adapted for automotive use in the early days of the sport of drag racing. The model name of these units delineates their size; i.e. the once commonly used 6-71 and 4-71 blowers were designed for General Motors diesels having six cylinders of 71 cubic inches each, and four cylinders of 71 cubic inches each, respectively. Current competition dragsters use aftermarket GMC variants similar in design to the -71 series, but with the rotor and case length increased for added pumping capacity, identified as the 8-71, 10-71, 14-71 etc.
The volumetric efficiency of the Roots-type blower is very good, usually staying above 90% at all but the lowest blower speeds. Because of this, even a blower running at low efficiency will still mechanically deliver the intended volume of air to the engine, but that air will be hotter. In drag racing applications where large volumes of fuel are injected with that hot air, vaporizing the fuel absorbs the heat. This functions as a kind of liquid aftercooler system and goes a long way to negating the inefficiency of the Roots design in that application.
Blower Design Images
