The wastegate actuator is a spring/diaphragm combination that is the mechanical control of the wastegate. The wastegate is a small “door” in the turbine housing, that opens and closes, allowing hot exhaust to escape from the turbine inlet to the turbine outlet, essentially creating a bypass, allowing exhaust to circumvent the turbine wheel (read more about the turbocharger). This process is what controls the actual boost that is delivered to the engine.
The actuator works in combination with our electronics (EBC) to control boost. The spring portion of the actuator holds the wastegate door shut, until a certain pressure. The diaphragm portion of the actuator responds to pressure changes (controlled by our electronics) in response to boost control. For example, a black actuator is a 6-lb actuator. Using this 6-lb actuator, without EBC, would force the system to make 6 psi of boost. However, with our EBC, we’re able to leverage the diaphragm portion of the actuator to control boost, within a range, in this example from 6-10 psi. (Read more in Electronic Boost Control.)
The actuator also controls the rate of increase in boost pressure. A stiffer spring will build more boost, more quickly, while a softer spring will create a more linear power curve.
Choosing the correct wastegate actuator is essential. You want to properly select an actuator so that your boost setpoint is in the middle of the actuator’s effective range. This allows the actuator to accurately control boost for your application. If your boost setpoint drops below actuator minimum, you will be making more boost than is called for, which means additional power. The owner needs to manage this by using the proper octane to prevent detonation, and the proper clutching to prevent an over-rev scenario.