Now you know that a turbocharger compresses the air and make it higher in pressure. But as the rpm increase,the compression from the compressor is also increased.This is bad for the engine cause engine can only take a certain amount of predetermined pressure before falling apart. This is where the wastegate comes in play.
A wastegate is almost similar to a blow off valve(bov) except for its function and the way it is being used. A bov will open to release the trap pressure while the wastegate open to regulate the air flowing to the turbine.
What is a wastegate?
A wastegate is a pressure activated valve which the input is taken via vacuum hose from the inlet manifold before the throttle body. This mean that the pressure supplied to the wastegate is actually the boost pressure that is build by your compressor. The function of a wastegate is to maintain a certain predetermine boost pressure and prevent the compressor from compressing the air further more.
There are two types of wastegate, which is an external wastegate and internal wastegate(commonly known as actuator).
Where is it located? The external wastegate is usually installed at the extractor or exhaust manifold just before the turbine while an internal wastegate or actuator is integrated inside the turbo unit itself.
How does it works?
A wastegate or actuator is set by the factory to maintain the boost pressure at the certain figures let say 1 bar or 14.7psi. Whenever the pressure reaches 1bar,the pressure will oppose the spring in the wastegate, this in turn will open the wastegate.By opening the wastegate,the air which is suppose to turn the turbine is bleeded to atmosphere or bypassed to the exhaust gas. This in turn will cause the turbine to maintain at a constant speed, hence the compression of the compressor will remain constant and maintain at the boost pressure at 1 bar. When the boost pressure drops below 1 bar,the wastegate will close and the turbine is allowed to rotate at any speed.
Is wastegate important? Yes,a wastegate is a mean of controlling your boost pressure.If your boost pressure increase excessively, it may cause your engine to run lean and makes your engine run very hot(less cooling by fuel) and this may lead to your piston ring,gasket,piston and other internal part to melt and destroy your engine. Other than melting it,it may also blow up the engine if the engine cant withstand high pressure.
External wastegate vs Internal wastegate
Actually both serve the same purpose which is to maintain the boost pressure. Internal wastegate or actuator is inside the turbo unit itself and it comes from the manufacturer. The actuator ability to regulate the pressure is limited due to the small valve size.
So whenever your engine has been modded and set to be run at higher boost pressure, an external wastegate is required as the internal wastegate cant bleed enough air in order to maintain the turbine speed.