Supercharging is also known as forced induction, a technology that’s been used for more than 100 years in applications ranging from blast furnaces to diesel generators. But during the Second World War as battles raged over Europe and the Pacific, supercharging came into its own, giving aircraft the horsepower edge in an increasingly desperate struggle. And in the thin air at 20,000 feet, a pilot’s engine needs all help it can get. When an engine is normally aspirated (draws in air without assistance) it relies on atmospheric pressure (at sea level approx 14.7 pounds or 1 bar) to push the air into the manifold (running under vacuum) and into the combustion chambers (cylinders). Due to internal restrictions along the air path, the normally aspirated cylinder is never able to completely draw in a full charge of air/fuel mix. In general a supercharger is anything that will force more air, or air/fuel mixture, into the cylinders of an engine at a faster rate than would be drawn naturally by the suction of the pistons during the intake stroke (putting the engine into positive pressure). This process is used to increase power and torque of an engine.
Supercharger Types
There are several fundamental designs of superchargers (roots, screw, vane, rotary, axial flow and centrifugal). Each design has its advantages and each are differently suited to different types of application. The most commonly used today for aftermarket supercharger kits are the roots and centrifugal. The roots units, ideally need to be mounted on the plenum chamber but the centrifugal type is not restricted in this way. However all supercharger units need to be mounted to take a drive from the engine crank pulley by a serpentine belt.
Supercharging Parameters
Performance modifications /customization to a vehicle are termed as ‘Aftermarket’ or ‘Retro-fitting’. When retro fitting a supercharger, an important factor is the natural compression ratio of an engine. Supercharging as an aftermarket technique is typically setup to create a 40% power increase. More power can be produced if the compression ratio is suitable. VF-Engineering engineers kits to produce a modest 6-9 lbs of boost. Subject to long term testing on all prototype cars, this is considered to be a safe level for the stock engine. Where high levels of boost are used, lowering the charge temperature is desirable to reduce detonation and retain safe operating parameters. VF-Engineering attains this by using an air to water intercooler.
Why Supercharge?
Compressed air contains a greater amount of oxygen molecules which improves the fuel combustion cycle. Compressed air contains a greater amount of oxygen molecules which improves the fuel combustion cycle. However, this requires that the fuel mixture and ignition cycles be altered/increased to suit the increased volume of oxygen. Retro-fitting a supercharger usually provides a much larger power gain compared to other aftermarket modifications such as capacity increasing which is also expensive. Supercharging with a centrifugal supercharger is less obtrusive to the vehicle and reversibility is simple to incorporate into its design.
Supercharger Efficiency
A centrifugally supercharged engine will operate under vacuum until the ECU determines the motor is at wide open throttle (full throttle). At this point the engine goes into positive pressure (onto boost). Up to this point the fuel consumption is not affected. When driving hard and on full throttle the supercharged engine will be creating more power and hence using a greater amount of fuel. Fuel consumption usually increases in the region of about 10% depending upon how often you drive under boost and the type of supercharger you have fitted.
