Manual Boost Control
A manual boost controller is a simple mechanical and pneumatic control to allow some pressure from the wastegate actuator to escape or bleed out to the atmosphere or back into the intake system. This can be as simple as a T-fitting on the boost control line near the actuator with a small bleeder screw. The screw can be turned out to varying degrees to allow air to bleed out of the system, relieving pressure on the wastegate actuator, thus increasing boost levels. These devices are popular due to their negligible cost compared to other devices that may offer the same power increase.
Additionally, another type of manual boost controllers use a ball and spring to control the amount of boost. This is installed with one boost signal line coming from the intake somewhere after the turbocharger, and one boost signal line going to the wastegate. A knob changes the force on the spring which in turn dictates how much pressure is on the ball. The tighter the spring, the more boost that is needed to unseat the ball, and allow the boost pressure to reach the wastegate actuator. There is a bleed hole on the boost controller after the ball, to allow the pressurized air that would be trapped between the wastegate actuator and the ball after it is seated again. These type of Manual boost controllers are becoming vastly popular since they do not provide a boost leak, allowing faster spool times and better control than a "bleed type" boost controller.
Generally a manual boost controller will not be accessible from inside the car, though some are designed to be. An installation that allows access from inside the car (as opposed from inside the engine compartment) is more complex, as the tubing must be longer and a hole must be drilled. It is possible and beneficial to use two manual boost controllers at different settings with a solenoid to switch between them for two different boost pressure settings. Some factory turbocharged cars have a switch to regulate boost pressure, such as a setting designed for fuel economy and a setting for performance.
Manual boost controllers do not solve partial throttle/full boost, drivability, and response or lag issues. They can be used in conjunction with some electronic systems.
Read more about this topic: Boost Controller
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