Yeah... it took me a long time to suss out why the GFB valve would not work. It wasn't until I started thinking in terms of absolute pressure rather than vacuum, that it became clear. The dischanrge of the s/c is connected to the intake manifold, and the GFB gets its signal from the discharge manifold. Being a belt driven positive displacement s/c, manifold pressure drops virtually instantaneously when the throttle snaps closed, so no residual pressure to blow a valve open.
Thus the GFB has the same pressure under the piston from the manifold as it has on top of the piston from the manifold pressure signal line. The area on top of the piston is greater than the area under the piston (plus the spring) and there is no way that it can open. Doesn't matter what the manifold pressure is... that fucker will not open. The tech guy at GFB stopped talking to me when I pointed this out to him
Its a closed system independent of atmospheric pressure. To make it work as expected, you need to have an actuator diaphragm open to atmosphere on one side. THEN, you have 15psi available to assist in opening the valve when there is less than atmospheric pressure on the other side of the diaphragm. If you used the butterfly type valve pictured higher in this thread, then that would have worked as you suggest.
As far as the function of the bypass is concerned, it serves to equalise the pressure before and after the s/c. And since the s/c is always pumping, I'd say flow would be from the discharge side to the intake side. The ISCV admits air on the intake side. Car runs at about 60kPa(abs) at 100km/h, so I have changed the solenoid switching point to 80/75kPa and will see how that feels.
Cheers... jondee86
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