Superchargers are mechanically driven by the engine, using a belt or chain. This means they can provide boost immediately as soon as the engine starts and will generate boost in a linear fashion as engine speed increases. However, the downside of superchargers is that they always turn, regardless of whether or not the engine needs boost, which can be parasitic and reduce engine efficiency.
Turbochargers, on the other hand, are powered by the exhaust gas from the engine. This means they take some time to spin up, resulting in turbo lag. However, once they are up to speed, they can generate far more boost than a supercharger and are inherently more efficient since they utilize waste energy.
Combining a supercharger and turbocharger can mitigate the weaknesses of each individual system. The supercharger provides immediate boost, while the turbocharger provides more significant boost at higher engine speeds. This can result in a very broad torque curve and increased engine performance.
It is important to note that supercharging and turbocharging together is not a simple matter of "adding them on" to an engine. Proper tuning and engineering is required to ensure the two work in conjunction with each other and not against each other. This is why very few production vehicles have these twin-charging systems.
