Wastegate

A wastegate is a valve that diverts exhaust gases away from the turbine wheel in a turbocharged engine system. An external wastegate is a separate self-contained mechanism typically used with turbochargers that do not have internal wastegates. An external wastegate requires a specially constructed turbo manifold with a dedicated runner going to the wastegate. The external wastegate may be part of the exhaust housing itself. External wastegates are commonly used for regulating boost levels more precisely than internal wastegates in high power applications, where high boost levels can be achieved. External wastegates can be much larger since there is no constraint of integrating the valve or spring into the turbocharger and turbine housing. It is possible to use an external wastegate with an internally gated turbocharger. This can be achieved through a specially designed bracket that easily bolts on and restricts the movement of the actuator arm, keeping it from opening. Another route involves welding the internal wastegate shut which permanently keeps it from opening, but failure of the weld can allow it to open again.A 'divorced' wastegate dumps the gases directly into the atmosphere, instead of returning them with the rest of an engine's exhaust. This is done to prevent turbulence to the exhaust flow and reduce total back pressure in the exhaust system. A Divorced wastegate dumper pipe is commonly referred to as a screamer pipe due to the unmuffled waste exhaust gases and the associated loud noises they produce.The simplest control for a wastegate is a mechanical linkage that allows the operator to directly control the wastegate valve position. This manual control is used in some turbo-charged light aircraft.Wastegate sizing is inversely proportional to the desired level of boost and is somewhat independent of the size or power of the engine. One vendor's guide for wastegate sizing is as follows: