As you might already know, internal combustion engines are massive air pumps. If you can pump more air in and out of the engine, you can effectively make more torque and more power. Getting more air into the engine can be done by improving the airflow of components like the intake manifold or cylinders, or you can simply just force more air into the engine with a compressor.
Where They Came From
If you’ve spent more than two seconds on YouTube looking at car videos, you’ve probably come across videos of crazy high-horsepower cars with giant spoily boi turbos. You probably didn’t know, but turbochargers were originally known as turbosuperchargers because they’re technically another kind of supercharger.
The whole idea of superchargers started back in 1860, when two brothers patented an air mover for use in blast furnaces. This air mover designed by Philander and Francis Marion Roots was later used on the very first two-stroke engine made by Dugald Clerk. Fast forward to 1885, and the idea of placing a roots style supercharger was patented by Gottlieb Daimler.
Although you’re probably used to seeing American muscle cars with massive roots style blowers, the first production vehicles to use a roots style supercharger were actually from Mercedes. The models which used the supercharged engine were identified with the Kompressor name, something which Mercedes still uses to this day.
Fast forward to today, and there are three different types of superchargers used in the automotive industry: roots, twin-screw, and centrifugal. They all used different methods of forcing more air into the engine, however, they’re all mechanically driven. Which more air being forced into the engine, more fuel can be added and larger combustion is created, resulting in more.
Of the three types of superchargers that are available, Roots is the oldest design. Inside a Roots blower, you’ll find two meshing lobes. Depending on the Roots supercharger, these lobes can have different shapes or different amounts of twist some of them have no twist at all, however, most automotive Roots supercharger have twisted lobes to reduce vibration.
One lobe spins clockwise, while the other spins counterclockwise. Air gets trapped between the lobes and forced to the walls of the housing and out of the other side. It should be noted that the meshed lobes of each rotor do not touch each other, however, the smaller the gap the better. With this design, low-end torque is massively increased, but the downside to a Roots blower is that they are massive and very heavy, and they are very inefficient.
Many Roots style superchargers you’ll see on old-school hot rods and muscle cars are not intercooled. It also takes a massive amount of power to even spin a Roots supercharger in the first place. On top of that, the Roots design is thermally inefficient, resulting in pretty hot charge air temperatures. With hot air temperatures come less power, since hot air is less than cold air, and a higher chance of detonation.
Moving on from the Roots supercharger we have the twin-screw supercharger which works in a roughly similar fashion. Like a Roots supercharger, the twin-screw supercharger has two rotors, however, the way they work is quite a bit different. Where a Roots supercharger takes air from the top and forces it downward, the twin-screw takes air from either the front or the rear, and forces it from one side of the supercharger to another, and then down into the engine.
With a twin-screw supercharger, the tolerances are very tight, so the air doesn’t bypass the rotors like it can on a Roots style supercharger. It works by using a male rotor and a female rotor. As they spin, the male rotor forces air further down the female rotor until it reaches the output location where the compressed air exits the supercharger and enters the engine.
Compared to a Roots blower, a twin-screw supercharger is much smaller, takes less power to spin, it’s more thermally efficient and easier to intercool. Like a Roots supercharger, the twin-screw makes a lot of low-end power and has awesome throttle response, creating boost almost instantaneously.
Both roots and a twin-screw are known as a positive displacement supercharger and move a fixed amount of air per rotation, where a centrifugal supercharger output is not fixed per rotation.
If you’ve ever seen a centrifugal supercharger, you might think they look a lot like a turbocharger, and that’s because they work similarly. Of course, a turbocharger is driven by exhaust gas, and a centrifugal supercharger is driven mechanically, but they both an impeller to push air.
Centrifugal superchargers are geared to spin to impeller a certain amount of times per rotation of the pulley on the front. The design of a centrifugal supercharger sacrifices low-end power, but once you get them spinning they can move a massive amount of air and create tons of boost.
One of the big benefits of a centrifugal supercharger is the ease of using an intercooler. While Roots and twin-screw superchargers are typically mounting right on the of the engine or they’re directly mounted to the intake manifold, a centrifugal supercharger is typically mounted to the front of the engine, making it way easier to route the compressed air through an intercooler.
Depending on your application, each type of supercharger has its pros and cons. For the most part, Roots style superchargers aren’t used in modified street cars because of their massive size, weight, and inefficiency. Applications, where you’ll typically see a Roots style supercharger, are on drag cars.
Centrifugal superchargers are very popular for street applications and can easily make a massive amount of power, but for those who want tons of low-end power, a twin-screw is probably a better option.