Ever since early hot rodders took their cues from World War II fighter planes and adopted belt-driven forced induction as a proven way to generate more power from less engine, the supercharger has earned its place in the American pantheon of power. The image of a bug catcher intake raking up over the hood atop a roots-style supercharger has firmly established itself in the visual lexicon of automotive performance.
Down to the Roots
The roots-style supercharger became the standard of forced induction over Potvin, or centrifugal-style superchargers, thanks to used examples being readily available on GMC diesel trucks back in the '50s, and even today. There are great advantages to using a roots-style supercharger to create horsepower. Instant power comes right off idle thanks to its ability to develop boost at lower engine rpm. This is a good quality for getting a vehicle moving from a dead stop in a hurry -- perfect for something like drag racing, or even everyday driving.
Another great quality of supercharging is that you don't necessarily have to spin the engine within an inch of its life to make big power. Thanks the supercharger's ability to compress air and fuel before it enters the combustion chamber, a little horsepower suddenly turns into a lot, with only minimal effort. The result is a small block or four-banger that looks like a Chihuahua, but acts like a Great Dane, so to speak. Oddly enough, the roots-style blower was originally invented by Francis Roots in 1860 to ventilate mineshafts and the like. It took Gottlieb Daimler of Mercedes-Benz fame to finally bolt one up to an engine in 1900. While this early effort was not hugely successful, the stage was set for further forced induction.
A roots-style supercharger amplifies engine power through two sets of counter rotating lobes that, as they spin, force air and fuel down into the engine. The lobes are the working part of the rotors, which spin inside a housing and are connected to bearings at either end of the housing to prevent them from smashing into each other as they spin. A pulley and belt is connected to a set of gears inside the front bearing plate, the belt draws engine power to make the lobes spin. The supercharger, therefore, spins in direct proportion to engine rpm, with boost levels controlled by the ratio of the pulley attached to the supercharger drive gear. Larger wheels turn the small wheel faster, for example.
The main difference between a supercharger and a turbocharger is that the supercharger takes its power directly from the engine via a pulley, while the turbocharger spins by way of engine exhaust powering an impeller. There are advantages and disadvantages to both methods of forced induction -- discussion that could fill many chapters of many books.
All this, of course, brings us back to Francis Roots and Gottlieb Daimler, two hot rodders with desires for greater speeds, and the supreme way to extract more horsepower out of an engine. Lucky for us, the solution here is simple: Squeeze more fuel and air into it by way of supercharging or turbocharging. That said, there is no great secret to making big power with any engine, fuel and air combined with spark is the basic recipe for horsepower; it's up to the cook to make it work right. With many manufacturers adopting the hot rod credo of generating more power from less engine, there is sure to be a lot of supercharged cooking to come.
Follow along with the steps for an inside look into a roots-style supercharger assembly.
At the heart of the roots-style supercharger are the rotors. Here the rotors get coated with graphite for final assembly.
The case contains the spinning rotors along its length. Before assembly, the surfaces are machined to specification.
The counter-rotating rotors take air in through the inlet, and force it down into the engine through the outlet.
Here the rotors are fitted into the case. The lobes on the rotors spin into each other and compress the incoming air.
Since superchargers operate with tolerances in the realm of a few thousandths of an inch, all components are meticulously measured.
Clearance measurements determine which components need to be machined, and how much.
The rotor gears reside in the front bearing plate. The drive gear runs off engine power via a pulley, and is subjected to the most stress.
Once everything checks out, the supercharger is assembled one last time, and is then ready for action.
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