Vivid Racing carries many different types of manual and electronic boost controllers.  Please read some technical information below about how boost controllers work and what they are used for.  You can view our entire boost controller catalog here -  http://www.vividracing.com/catalog/electronics-boost-controls-c-4339_4344.html

Manual Boost Controllers -
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.

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.

Electronic Boost Controllers -
Electronic boost control adds an air control solenoid and/or a stepper motor controlled by an electronic control unit. The same general principle of a manual controller is present, which is to control the air pressure presented to the wastegate actuator. Further control and intelligent algorithms can be introduced, refining and increasing control over actual boost pressure delivered to the engine.

At the component level, boost pressure can either be bled out of the control lines or blocked outright. Either can achieve the goal of reducing pressure pushing against the wastegate. In a bleed-type system air is allowed to pass out of the control lines, reducing the load on the wastegate actuator. On a blocking configuration, air traveling from the charge air supply to the wastegate actuator is blocked while simultaneously bleeding any pressure that has previously built up at the wastegate actuator.

Boost Controller Details -
Control for the solenoids and stepper motors can be either closed loop or open loop. Closed loop systems rely on feedback from a manifold pressure sensor to meet a predetermined boost pressure. Open loop systems have a predetermined control output where control output is merely based on other inputs such as throttle angle and/or engine RPM. Open loop specifically leaves out a desired boost level, while closed loop attempts to target a specific level of boost pressure. Since open loop systems do not modify control levels based on MAP sensor, differing boost pressure levels may be reached based on outside variables such as weather conditions or engine coolant temperature. For this reason, systems that do not feature closed loop operation are not as widespread.

Solenoids are driven by pulse-width modulation as they are binary state devices, either allowing air flow or blocking it between any two given ports. By modifying the pulse width at a sufficiently high frequency, average air pressure over time can be controlled. Solenoids may require small diameter restrictors be installed in the air control lines to limit airflow and even out the on/off nature of their operation.
Stepper motors allow fine control of airflow based on position and speed of the motor, but may have low total airflow capability. Some systems use a solenoid in conjunction with a stepper motor, with the stepper motor allowing fine control and the solenoid coarse control.

Many configurations are possible with 2-, 3-, and 4-port solenoids and stepper motors in series or parallel. Two port solenoid bleed systems with a PID controller tend to be common on factory turbocharged cars.

Advantages of Boost Controllers -
Since less positive pressure can be present at the wastegate actuator as desired boost is approached the wastegate remains closer to a completely closed state. This keeps exhaust gas routed through the turbine and increases energy transferred to the wheels of the turbocharger. Once desired boost is reached, closed loop based systems react by allowing more air pressure to reach the wastegate actuator to stop the further increase in air pressure so desired boost levels are maintained. This reduces turbocharger lag and lowers boost threshold. Boost pressure builds faster when the throttle is depressed quickly and allows boost pressure to build at lower engine RPM than without such a system.

This also allows the use of a much softer spring in the actuator. For instance, a 7 psi spring together with a boost controller may still be able to achieve a maximum boost level of well over 15 psi. The electronic control unit can be programmed to control 7 psi at half throttle, 12 psi at 3/4 throttle, and 15 psi at full throttle, or whatever levels the programmer or designer of the control unit intends. This partial throttle control greatly increases driver control over the engine and vehicle.

Dangers in Use -
Installing a boost controller in a vehicle that is already well tuned (such as a factory turbocharged car) may allow higher boost pressure than tolerable by the engine or turbocharger reducing life and reliability. Care should be taken to avoid exceeding the limits of any the engine systems components such as the engine block, fuel injectors, or engine management system. This is as true with boost control as it is with fuel and timing controls or any number of other engine system modifications.

In particular, users may find the extremely low cost and ease of adding a manual boost controller a particular draw for extra power at low cost compared to more comprehensive modifications. Users should carefully consider how installing any boost controller may affect and interact with existing complex engine management systems. Additional boost levels may not be tolerated by the existing turbocharger, causing faster wear. Fuel injectors or the fuel pump may not be able to deliver additional fuel needed for higher air flow and power of higher boost pressure. Or the engine management system may not be able to properly compensate for fuel or ignition timing, causing knock and/or engine failure.