What is a wastegate?
A turbocharger wastegate is a small valve, which is used to control the amount of boost the turbo makes. It opens at a predetermined limit, to allow surplus exhaust gas to bypass the turbine and disappear straight down the exhaust pipe once the boost limit is reached.
Most engines can handle a small amount of additional boost but the temptation is to keep going, as it's relatively easy power. But there is only so much boost that a turbo can produce. For a given turbo, the boost pressure is dependent in the amount of exhaust gas going through the turbine. This is controlled by a small valve, known as the wastegate. This opens at a pre-determined limit to allow surplus exhaust gas to bypass the turbine and disappear straight down the exhaust pipe once the boost limit is reached.
Normally, a wastegate will have a spring on one side of the diaphragm and boost pressure on the other side. At the point where boost exerts force greater than the spring pressure, the gate opens to bleed off the exhaust gases. Reducing the pressure seen by the wastegate or increasing the strength of the spring will make the wastegate open at higher boost pressure hence the engine will get more boost and power. However, the limit to this is what the turbo can handle, both physically and from the air flow point of view. If too much exhaust gas is sent through the turbine, the unit can over-speed, which puts mechanical stresses on it and can lead to all sorts of problems, such as breaking shafts or compressor wheels failing.
In Addition, the air flowing into the engine can start to get very unpredictable, a situation known as "surge". This can have very detrimental effects on the engine's internals and power delivery. The solution is to tailor the turbo itself to the requirements, and if necessary replace a standard version with one designed for the job. This can be a physically bigger turbo or a different turbine and compressor characteristics.
Internal Wastegate
There are two types of wastegates the first one is an internal wastegate. An internal wastegate is a component on the turbo itself. The gate is opened via an actuator which is a diaphragm type system. Excess exhaust is then fed directly into the exhaust system.
External Wastegate
They may also have what is called an external wastegate. An external wastegate is separate from the turbo unit and does not require an actuator.
