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Also to be noted is the way in which boost control is achieved, depending on the type of wastegate used. Typically manual "bleed type" boost controllers are only used on swing type (single port) wastegate actuators. To increase boost, pressure is taken away from the actuator control line, therefore increasing the turbo output pressure required to counteract the controllers leak-lowered pressure acting on the wastegate. Dual port swing type wastegate actuators and external wastegates generally require electronic boost control although adjustable boost control can also be achieved on both of these with an air pressure regulator, this is not the same as a bleed type boost controller. To increase boost with an external or dual port wastegate, pressure is added to the top control port to increase boost. When boost control is not fitted, this control port is open to the atmosphere.
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== Manual boost control ==
[[Image:manualboostcontroller.jpg|thumb|220px|A simple manual boost controller. A small screw is located in the top of the aluminum body to adjust bleed rate. This model is placed in the engine bay; however, the vacuum line could be extended to allow it to reach into the passenger compartment.]]
A bleed-type manual boost controller simple mechanical and [[pneumatics|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.
A ball & spring type boost controller uses the force of a spring acting against the boost pressure to control 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 to escape that would otherwise be trapped between the wastegate actuator and the ball after it is seated again. These type of Manual boost controllers are very popular since they do not provide a boost leak, allowing faster spool times and better control than a "bleed type" boost controller.<ref>http://www.fiercecontrollers.com/uncategorized/bleed-or-ball-and-spring-manual-boost-controller/</ref>
There are several different designs of ball-and-spring controllers on the market that range greatly in terms of cost and quality. Common body materials are brass and aluminum vary from inline to 90 degree designs. Another design aspect is the ball valve seat which is critical for performance stability.<ref>https://www.precisionballs.com/ball_valve.php</ref>
Generally a manual boost controller will not be located within the cabin of the vehicle as the lengthy vacuum piping run between the turbo/wastegate & controller can introduce response issues into the system. It is possible 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 in automobiles|fuel economy]] and a setting for performance.
Manual boost controllers cannot be used to set a specific boost level at a given throttle position (& therefore be used to optimise driveability & control issues), although a ball-spring type boost controller does allow the boost threshold to be as low as is possible on a given engine configuration, and also keeps turbo spool as fast as is possible as the wastegate remains completely shut until the desired boost pressure is reached, ensuring 100% of the exhaust gases are diverted through the turbocharger exhaust turbine.
They can be used in conjunction with ''some'' electronic systems.
== Electronic boost control ==
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