What's the restrictor do? How much smaller than the line ID?

Even with a straight line from the compressor to the open port on the actuator, it should show an improvement. Right now I get a typical curve to about 4.5psi at which point I have linear boost rise to 7psi+ at redline.

What about a "dumb" solenoid on the close port signal line that closes with a pressure switch? That might take some work to tune with an EBC.. probably produce an unmanageable spike.

 

Without a restriction the bleed will have to pass a lot of air to work.

How about getting one of those solenoids with a switching output? That way when deactivated, all boost goes to one side (minimum boost), when at 100% duty, you get infinite boost.

 

Switching output - as in a solenoid that can send the pressure to port A, B or C? rather than one that does just port A or B - in my case A being to the actuator and B to atmos.

My concern about removing the pressure instantly from the close side of the actuator, is that the valve will surely come open- and open before the ecu has set into closed loop. If I leave the pressure there, then boost control can work with it as though it was a stiffer/helper spring.

 

Correct. A solenoid with input 'A', and will direct the pressure to either 'B' or 'C'. You do this 20x-50x a second and the problem you describe won't happen. Such a setup needs 2 small bleeds, one between the solenoid and each wastegate port.