Superchargers are air pumps that increase the air flow to the engine, allowing for increased combustion and power. They differ from turbochargers in that they are belt driven by the crankshaft, whereas turbochargers are driven by the flow of exhaust gases.

There are three common types of supercharger in use today: Roots, twin-screw, and centrifugal.

Roots Supercharger

Also known as a positive displacement supercharger, the Roots delivers a fixed amount of air per revolution. Roots type blowers utilize a pair of meshed rotors to pump the air around the outside of the casing and down into the intake manifold. Typically, each rotor has from 2 to 4 lobes and is gear-driven. ​

One of the smaller, more efficient Roots type blowers is the Eaton TVS (Twin Vortices Series), which can reach thermal efficiency ratings of up to 75%. The TVS is available on the Corvette ZR1 and the Rousch Stage 3 Mustang and on several other high performance vehicles as well.

The advantages to a positive displacement supercharger include boost throughout the complete RPM range, extreme reliability, and the greatest potential for gain. Because of their low-RPM boost, Roots superchargers are the most often used in applications requiring high torque. Roots blowers are the simplest in design, and because of their low rotational speeds, they offer exceptionally reliable performance.

The disadvantages to the Roots type blower include reduced performance at the upper end of the RPM range, high discharge temperatures, and a weight disadvantage. The higher temperature of the discharged air requires the use of an intercooler to avoid damage to the engine. Additionally, hotter air is not as dense as cool air, so combustion efficiency is reduced by the high temperature.

Twin Screw Supercharger

Also known as Lysholm superchargers, the twin screw blower has an axial air flow that compresses the air as well as pumping it into the intake. Twin-screw blowers develop much less heat than Roots blowers, but like a Roots blower deliver boost throughout the RPM range of the vehicle. The twin-screw configuration was developed from the Roots supercharger, but designed with street use in mind.

Advantages of the twin-screw design include great reliability, high low-RPM power, and cooler discharge temperatures than Roots units. Twin screw units also require less energy to turn the rotors, which increases the power available to the rear wheels.

However, the power curve from a twin screw supercharger is relatively flat, which leads to boost falling off at higher RPM ranges. Maintaining the air flow at higher engine speeds can also be a problem, and the precision nature of its design adds to the cost of manufacturing.

Centrifugal Supercharger

Centrifugal superchargers attach to the front or side of the engine instead of the top and use an impeller to compress the air. In terms of design the centrifugal blower is similar to a turbocharger, but like all superchargers, they are belt driven. Changing the boost is accomplished by swapping the impeller rather than a pulley. Because they are inexpensive and relatively easy to mount, centrifugal chargers are the best selling type of blower.

Centrifugal superchargers offer a great deal of flexibility for boost adjustments, run cooler than other types of blower, and install quickly. They provide higher boost in the upper RPM range than positive displacement units as well.

The biggest disadvantage to the centrifugal blower is low boost pressures at the bottom of the RPM scale. This is because of the way they produce boost: a centrifugal blower lacks a linear relationship with the engine speed, and are usually set to provide maximum boost at higher RPMs, which affects low speed performance.

By Vanessa Wilson