I believe that the ECU receives feedback from the Boost Solenoid as it regulates boost. Because of this when a MBC is used in instead of the Boost Solenoid the ECU sees no feedback and retards timing at high rpms. With this setup, the MBC after the Boost Solenoid, the ECU still receives feedback and allows for maximum power at full boost.
So why not just use a MBC after the Boost Solenoid and forget about a dual stage device? I have found that over time the ECU realizes that it is not in complete control and backs off the power at high rpms. With this setup I have found myself letting the ECU control boost about 90% of the time. In the cases when I want more power I switch over to the MBC and get an extra kick in the pants.
I use MBC control primarily during circumstances when I want quick spool up and low-end torque. And with this setup I can keep the MBC in control to redline and still have max power without the typical timing retard that usually occurs with MBC control.
I give an example of a wide open throttle accelerations on my website.
ECU control has max boost at 17 psi. The button is pushed to close the solenoid and the MBC takes over. Boost quickly rises to 20 psi and there is a noticeable power increase.
Eric
