Just been reading up on dual solenoid boost controllers, and came across this thread: http://www.sr20-forum.com/informati...ost-control-wastegates-how-turn-up-boost.html Where should I get my wastegate boost source from? This is a common question so it is time to go over the options. First off, you only want the wastegate to see positive pressure (boost). Under no circumstances should the wastegate ever see negative pressure or vacuum unless you're a mad scientist doing something crazy in which case you don't need my help. There are two reasons for this. 1) Allowing a diaphragm-type wastegate to see boost and vacuum in quick succession or vacuum at all will wreak havoc on the diaphragm. The diaphragm is not designed to see vacuum or cycle between vacuum and boost. I'm not sure how much this shortens the life of the diaphragm, but the wear is significant. 2) Even if you don't have a diaphragm-type wastegate, there is a more important reason not to let the wastegate see a vacuum signal. If you use a combination boost/vacuum source then there will be situations where you're trying to limit boost to the engine with the throttle plate but the turbo will be forced to create more and more boost. Think about what happens during a WOT shift. You have boost to the wastegate and it is fully open as you approach the redline. Then you lift off of the throttle which instantly pressurizes the system from the compressor to the throttle body. Hopefully your BOV or recirculation valve is now opening to prevent compressor surge. It is at this time that you want the turbo to stop creating boost. As the pressure in the intake system drops from the spike it experienced at throttle closing the wastegate should be open to reduce the chance of adding additional pressure to the charge pipes. If you have the wastegate plumbed to the intake manifold it will see vacuum this entire time and stay securely closed, promoting more boost in the charge system at the very moment you're trying to get rid of it. On some systems this can cause minor drivability issues and on other systems this can cause severe on/off throttle behavior and reduce your partial throttle control to almost nil. The worst situations happen during partial throttle closing situations. You're closing the throttle trying to reduce power output and creating a vacuum in the intake manifold, meanwhile the wastegate forced closed by the vacuum signal it is getting from the manifold so it tries to force more boost into the system. Transient throttle response gets quite messed up. I don't think many (if any) on here have ever questioned taking the reference for a boost controller install off the plenum. Discuss.