Supercharger calculations

Question

How to determine safe supercharged pressure and CFM for a motor cycle engine (fuel injected 149cc (9.31 cubic inches) 12.9 bhp?

Answer 1

There is no formula or calculations that you could run. Adding an aftermarket supercharger is more of a trial and error versus scientific calculation.

The reason there is no formula or calculation is because there are too many variables to account for.

In no particular order.

• Strength of the engine including but not limited to crank shaft, connecting rods, piston rings, head gasket, head bolts, intake manifold. Any of these components could be a weak link in the chain and fail.
• Ability to add enough fuel. This is generally limited by stock injectors, fuel pressure and fuel volume from pump.
• The ability of the control system to manage the boost. MAF (mass air flow) systems tend to be easier to modify keeping the old computer. Speed density systems require replacing the MAP sensor with one that can sense pressure well. An aftermarket control system may be required.
• Heat of the engine. Adding a supercharger will burn more fuel. More fuel generates more heat. The ability of the engine to reject that heat plays a big role. If the engine is air cooled it may overheat quickly. If it's liquid cooled does it have a water pump and is the radiator large enough.

There are probably other thins that i'm missing and/or forgetting.

The best advice I can give is;

1. Find a supercharger that fits. This may actually be the biggest challenge.
2. Figure out how your going to control the setup.
3. Slowly increase the supercharger pulley ratio until you have enough power or something fails.