Giant enhancement of the dyno performance with help of supercharger

Brent Ford Racing

The supercharger is based on a forced induction mechanism which squeezes more air into the engine, thereby creating more power. Unlike turbochargers, the boost power of supercharger is triggered mechanically by a belt-pulley where the rotational energy is drawn from the crank. Here I focus on the centrifugal supercharger because it is designed for high-rpm performance. The air (blue arrow) molecules are dragged by the supercharger turbine blades and then the air molecules discharge (red arrow) along the tangential direction.

Before purchasing a supercharger for your own engine, you need to check the pressure-ratio and flow rate. Otherwise, the supercharger may destroy your engine. 

There is a standard method to estimate the flow rate and pressure-ratio analytically. You may read the link below. 

https://roywchvehicle.blogspot.com/2019/11/your-turbocharger-your-choice.html   

For example, let's try to reinforce the Chevy 302 engine to 625 Horsepower (@flywheel) at 7000 RPM with help of a centrifugal supercharger. The calculated flow rate and pressure-ratio are 55 lb/min and 1.63, respectively (To read these equations, please read the link). There are numerous centrifugal superchargers on the market. It is important to read the compressor map so that the pressure-ratio and flow rate are located in non-choke and non-surge regions.

Compressor map: Vortech V2S supercharger

'Surge': Turbine rotates too slow (grey area - LHS)
'Choke': Turbine rotates too fast (grey area - RHS)
Black dot: Measurement 

The supercharger is driven by a serpentine belt-pulley where the belt ratio plays an important role to dyno performance.

Belt-ratio: diameter of crank pulley / diameter of supercharger pulley

The belt ratio of 1.6 means that the crank needs to rotate 576 degrees until the supercharger pulley completes 1 turn. Hence, a large belt ratio usually pushes the peak performance to lower rpm. In contrast, a belt ratio less than 1 usually weakens the engine output.

Measurement data

The air pressure is dropped by 3 psi across the intercooler and the gate limit is 10 psi. 

Despite supercharger may not be as competitive as turbocharger at red zone, supercharger does not suffer lag (i.e. how much time passes between the driver depressing the gas pedal and the engine's response) because the boost power is transferred from the crank.