Ohh and one last advantage of 4 port solenoid….
Almost ALL WG leaks air from our vacuum/pressure hose internally in the WG below the membrane and out through the valve guide clearance - this is from the pressure applied to the lower port - and the leak is regardless what brand I tested, it is how they are build. And it can be quite a lot actually, especially after some hours of use – you need to test after WG has had its first time run hot and no more grease sits between valve stud and valve guide. This is normal, however it is a leak, and it will show and make your boost disappear when you do an overall system leak test (not to compare with the above WG stand-alone pressure test). By running a 4 port solenoid valve you no longer care about this leak, as you only use the lower port AFTER target boost is achieved so now the leak become part of the closed loop bleeding process which the solenoid handles just fine.
With the 3 port valve setup you are still fighting against this leak in your lower WG port, and your compressor / inlet system will have to share this leak with the birds until target boost is reached
Try and put pressure under your first time driven/used WG lower port and you will learn how much boost leakage you have right there! Then do the same on the top port of wg, and you will see the advantage of 4 port valve using this port only when building boost to your inlet system. You will find a rock solid pressure reading on wg top port always!