to draw it. I suck at that [ http://pics.fullavit.com/4port/diagram.png ] The principle is that you run boost to the side of the diaphram without the spring when low boost is wanted. When you want to build boost boostpressure is shifted to the springed side. This way the springpressure + boostpressure holds the WG shut. Thats why you can build high boost with weak springs. This is practical i situations where you for example want to run, say 7 psi on first gear for traction but high boost on high gears where traction can be obtained. You would obviously need som kind of device to do that. For example an aftermarket ecu. (in my opinion you should run aftermarket anyways for various reasons)
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