3 ports better than 2? (boost solenoids)
 

Why are 3 port boost solenoids better than 2? What's the extra port for? Can they be interchanged easily?

i cant answer all off your question, but they are not recommended to be interchangeable, if youre on a standard map you shouldnt fit a 3 port

Basically 3 ports give better control over the pressure seen by the wastegate actuator.

In the later 2 port layout the 2 port acts as a variable bleed valve, allowing an ECU controlled amount of air to be diverted away from the pipe between the compressor outlet and the wg actuator.

In a 3 port layout the solenoid acts as a pneumatic switch, in the default 'closed' position air still flows from the compressor outlet to the wg actuator, but when 'open' the actuator is connected to inlet pipe (or atmos).

As Andy says without a remap you can't change the type of solenoid because the duty cycles required to control boost can be vastly different between the 2 methods.

Andrew...

thanks andy for filling in that gap in my knowledge

That makes sense. Thanks for that.