Well, yes and no. This was the first running of the motor since the bottom end was rebuilt. Nothing fancy just 97mm pistons. Everything else stock. The biggest change was the introduction of the MBC. Like I said, the MBC signal came from the intake charge pipe between the intercooler and the throttle body. I ran the MBC "wide open" so there should have been no pressure regulation occurring. This is how it tested on the bench as well -- where it worked as expected. Otherwise the ECU program was the same as was everything else.
Opening the MBC valve up all the way will give max bleed from the boost signal line and therefore hold the wastegate closed up to a higher pressure. Is that what you mean by "wide open?" If so, close the valve (loosen the screw).
Typically you would want to take the boost reference from the port on the compressor housing near the outlet. By referencing boost post-intercooler you are adding the pressure loss across the intercooler and charge plumbing, which will in turn raise the boost level as measured at the compressor housing outlet.
Where is your boost gauge signal reference - same place as MBC or somewhere else? Intake manifold, I'm assuming.
When we calibrate internal wastegate actuators the typical rule of thumb is to set the actuator preload so that the "boost setting" pressure value happens at 1.00mm (0.040") of actuator rod travel. To measure this we use a dial indicator set up parallel with the rod and measuring rod travel, right on the end, where it connects to the external crank arm on the turbine housing.
There are two force balances acting on a wastegate system: first, you have pre-turbine pressure acting to open the valve (inside the turbine housing), and post-turbine pressure on the other side of the valve. That pressure differential multiplied by valve area gives the opening force on the valve itself. The 2nd force balance is on the actuator rod. You have spring pressure acting to keep the rod retracted (wastegate closed) vs. actuator inlet pressure times diaphragm area acting to extend the rod and open the wastegate valve.
By increasing preload on the rod end you hold the wastegate closed up to a higher reference pressure, and offset the force vs. displacement curve, and reduce the available actuator rod travel. By swapping the actuator spring to a higher rate, you increase the opening pressure but don't affect travel, and more force (therefore more inlet pressure) is now required for the same displacement. By decreasing the inlet pressure signal on the diaphragm with an MBC or EBC, you delay opening the valve until a higher boost reference pressure is reached.
