Difference Between Roots, Twin

Roots-type units offer more power, while centrifugal superchargers are more versatile and compact.

Forced induction has always been an inseparable part of sports cars’ identity. If you love cars, you are more than likely to deeply enjoy hearing the turbo whistle or the scream of a spooling supercharger.

As you are already aware, forced induction systems in general work by pushing more air into the engine in order to make more power. However, there are numerous designs when it comes to different forced induction setups.

Turbochargers, which technically are a type of supercharger, work with the help of the exhaust gasses from the engine to spin a turbine, and as result, force air into the combustion chambers.

Superchargers, on the other hand, connect to the crankshaft via a belt. This means that the RPM dictates the speed at which the supercharger rotors spin. This has the benefit of seamless power delivery, both in low and high RPMs, eliminating "turbo lag".

Superchargers are commonly one of three following types: centrifugal, twin-screw, or Roots-type. Twin-screw and Roots-type superchargers function quite similarly, while the centrifugal supercharger has a unique design compared to the other two. It is important to know the difference as they provide distinct benefits and power delivery patterns.

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This system is the oldest supercharger design and was first patented by Philander and Francis Roots in 1860, and its initial usage was to act as a fan to ventilate mineshafts. After a while, Gottlieb Daimler patented the design for usage in internal combustion engines, and the first cars to have a supercharger were the Mercedes Kompressor models of 1923. They were also later used in two-stroke diesel engines and aircrafts from the second world war.

The Roots-type supercharger usually sits on top of the engine and receives air using the air intake and a belt coming from the crankshaft powers the rotors inside the supercharger and helps it blow huge amounts of air, which pass through an intercooler sometimes, into the engine.

This layout is almost the same as the twin-screw design, what makes them different are the moving parts inside the supercharger. In the Roots setup, there are two similar spinning rotors inside that seal the incoming air in between their lobes and against the body of the housing and release it into the engine. After that, the lobes of the two rotors lock onto each other, preventing air from coming back from the engine, as they move in opposing directions.

The rotors in some designs utilize seals on their lobes in order to be more efficient in the amount of air they force in. These seals, however, result in more friction and more heat, which translates into less reliability. This is why these sealed types of Roots superchargers are commonly present in Motorsports, especially in top-fuel drag racers.

The Roots-type supercharger adds a lot of power to the vehicle. However, its benefit compared to other forced induction options is the fact that the power delivery is instantaneous, the throttle response is smooth, and the torque curve is equally improved across all RPM. This happens because of the presence of rotors and how they push a fixed amount of air on each revolution.

An example of a modern car that has a Roots supercharger installed in its engine bay is the Dodge Hellcat (both Challenger and Charger models).

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The general layout of twin-screw superchargers is almost identical to the Roots-type. The only feature separating the two designs is the shape of the rotors. In twin-screw superchargers, one of the rotors is male, and the other is female, and they interlock as they spin. This might not sound like a lot at first glance. Although, this simple characteristic means that the interlocking mechanism compresses air as it travels through the space between the lobes.

Both the Roots-type and the twin-screw classify as "positive displacement" superchargers as they both provide a consistent power boost at all RPMs. Conclusively, the feature of a smooth and instantaneous power boost is present in both types. Yet, the twin-screw supercharger is often more efficient since it produces less heat compared to the Roots.

The 2022 Ford Mustang Shelby GT500 features a twin-screw supercharger made by Eaton.

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Turbochargers and centrifugal superchargers are very similar in design. The only distinction is that while turbochargers spin with the help of exhaust gasses, centrifugal superchargers have a turbine that connects to the engine using a belt and spins using the power from the engine.

This, however, means that these kinds of setups do not have the benefit of constant boost available with positive displacement superchargers. The centrifugal design takes a while to spool and will only add power and reach peak performance at high RPMs.

While the gradual boost buildup is not always ideal, the centrifugal supercharger has its own advantages, such as being drastically smaller than the positive displacement setups and being able to sit on the front of the engine instead of on top of it. This also allows for more versatile piping options and easier intercooler installments. The centrifugal supercharger also blesses the engine with a lot of power when it does get up to speed.

In conclusion, each type of supercharger serves a specific goal and has its pros and cons. The centrifugal supercharger is a better option for someone to install on their car as a modification, but positive displacement superchargers allow for a wider torque curve and an instant power boost from the get-go; There is something to like about each one.

Hamed is a literature student, writer, musician, and car enthusiast. His favorite topics to write about are cars, tech, and gaming. When he's not writing, he's either playing music or listening to it.