There are two types of superchargers: roots type and centrifugal type. Both types vigour air into the intake manifold. This is known as "forced induction." With more air being forced into the intake, more fuel must also accompany the air to keep the correct air-to-fuel ratio needed to properly run the car. This forced-air-and-fuel mixture effectively increases the volume of combustible material in the engine.
Centrifugal
The centrifugal supercharger works somewhat like a turbo charger, except that it is belt-driven instead of exhaust-driven. Because the engine turns at a certain speed, the centrifugal supercharger needs a way to force additional air into the intake. The "guts" of the blower include a step-up drive, which turns the impellers at a much faster rate, thereby forcing more air into the intake manifold. Once the air is drawn into the supercharger, the internal rotors (which are interleaved) compress the air before pushing it into the intake manifold.
Roots
Forced Air and Compression
In an unblown engine, air is sucked into the cylinders with a vacuum. The air-and-fuel mixture is compressed on the compression stroke, then ignited with a spark from the spark plug. Engines can be built with different compression ratios.A roots-type supercharger (this is what is commonly seen on top-fuel and funny cars) works like an air pump. Unlike the centrifugal superchargers, the air is not compressed in the supercharger. It pumps air into the intake, forcing the amount of fuel to increase to keep the mixture of air and fuel at its proper ratio. This mixture is then compressed within the cylinders.
The higher the compression ratio, the more horsepower and torque produced. A common compression ratio is 8:1. This means that the air-and-fuel mixture is compressed to about one-eighth of its volume before ignition. The supercharger forces more air and fuel into the cylinder, changing the compression ratio. The air is very dense, which requires more fuel. When the mixture is ignited by the spark plug on the combustion stroke, it provides an extreme amount of pressure in the cylinder, which in turn makes a larger explosion, giving you more horsepower and torque.
