RELEASING EXCESS PRESSURE

While a supercharger’s output is proportional to engine speed, a limit has to be reached. An engine may also be designed not to tolerate higher boost pressures than can be generated above, for example, 3000rpm; if more is provided in that case, the engine could detonate at higher speeds. Therefore, a separate valve tends to be attached, or mounted integrally, with the supercharger’s outlet, which forms a circuit between the outlet and inlet. When the supercharger is providing unwanted boost, such as on the overrun, the valve opens and boost pressure is recirculated; when the throttle is depressed again, the valve closes and instant boost is available – unlike a turbocharger, in which the turbine has to build speed again before maximum pressure is available.