A boost controller is a device which mechanically or electronically diverts intake manifold pressure away from a turbocharger wastegate prior to the development of predetermined boost levels. A wastegate safeguards the engine from excessive turbocharger boost by using manifold pressure to open a spring loaded relief valve and slowing the turbo down. A common problem with wastegates is that they often activate too early negatively effecting performance. A boost controller diverts wastegate control pressure away from the gate actuator until acceptable boost pressure levels have been reached. Boost controllers may be simple, manually set valves or sophisticated modules run by an electronic engine control unit (ECU). Boost controllers basically offset the tendency wastegates have to open before the turbocharger has had time to build optimal boost pressures. Wastegate springs are rated to open fully at a predetermined safe manifold pressure. Unfortunately they typically begin to open some time before this pressure is achieved. Boost controllers bypass some of the manifold gas which actuates the wastegate until the turbo has developed acceptable boost pressure values. The boost controller is installed in the wastegates actuator pressure line and consists of an adjustable bleed valve and an exhaust port. The bleed valve is adjusted so that some of the pressure in the line can escape relieving the pressure on the wastegate actuator. This allows the turbocharger to build up and maintain its boost pressure to optimal levels before the wastegate opens. The escaping pressure may be vented into the atmosphere or returned to the intake manifold. The valves used in boost controllers may be simple plunger types, spring and ball valves, or sophisticated solenoid operated variants. The basic operation remains the same though, and each type allows a preset amount of manifold pressure to be diverted away from the wastegate. Only after the turbo develops operational pressure will the wastegate open and bypass the exhaust gas. This valve would typically be situated under the hood adjacent to the wastegate. It may also be located in the passenger compartment by means of an extension pipe. More sophisticated electronic boost controller units feature electric solenoids which control the bleed valve. The solenoids adjustment of the valve is, in turn, controlled by the ECU. These electronic boost controllers are able to exercise a wide range of real-time control and are better suited to addressing turbo lag and response issues. This type of boost controller is often built into the turbocharger and can not be adjusted manually.
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