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This addresses MBCs installed in T5 systems, not applicable to T7's.
You guessed it, without the bleeder ports, the MBC becomes a check valve and the WGA will be pumped open and after one good run you will have a great deall of trouble getting back in boost with WG held open.
The bleeder hole provides a flow. That flow is analogous to an electrical current. The ball-spring is like a zener diode, it that there is no flow until the voltage is to a certain point. Once the ball-spring is overcome by pressure and flow starts, the ball-spring and its valve seat are a resistance to flow. The purpose of a MBC is to be a pressure divider, or in our analogy, a voltage divider. You only get a pressure or voltage drop when there is a flow or current and a resistance. So without the hole, there is no flow once the system is in steady state and then there would be not be a steady stage pressure drop. So without the hole, if you get on WOT and stay there, there would be an initial boost while the ball spring blocked flow, then the flow would start to move the WGA. While the WGA is moving there would be some flow and the pressure would be reduced. But after the WGA moved as far as it wanted to go, the flow would stop. You would have some boost, but then if you got off boost, you could not get back on boost unless the ball seat had a leak.
The bleed port is fundamental to the whole point of a simple bleeder valve or a ball-spring type MBC. It is not an afterthought for other features that you describe. There is a complex interplay between the bleed port size and the ball-spring tension. Thats for another day. Think about the MBC adjustment being a change in the flow pressure threashold and the resistance element. Both are tightly coupled. You cannot vary those things independant of each other. (Some MBCs have a ball-spring and a small inlet orifice for flow resistance. Those can overshoot as the flow to open the WGA is too slow. Those can be 'fixed' by drilling out the small inlet orifice to be wide open.)
So a MBC installed as an MBC will simply lock the WGA open. Doing that with an anticipator will simply let the MBC turned check vavle open the WGA faster on its one way journey.
The WGA is a negative feedback mechanism to control pressure. The MBC or BPC reduce the feedback pressure that the WGA sees, that increases the boost pressure. The WGA and WG are a simple pressure regulator.
posted by 207.43.195...
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