Usually having an internal wastegate limits the maximum achievable boost pressure to 2x the gate spring pressure.
Having an external wastegate allows for higher boost than that but only if its connected correctly.
Option 1:
Don’t use – it gives no advantage at all.
Option 2:
This is the right way to do it. At minimum boost setting the solenoid will be off and all the boost pressure will go to the bottom port while the top port will be vented to the atmosphere. At maximum boost the solenoid will be open and the boost pressure will also reach the top port helping the wastegate stay shut.
But is there another way to achieve even higher boost?
Yes, by using a 4 port solenoid!
Or even better, by using two 3 port solenoids!
Option 3:
In this case at minimum boost setting both solenoids will be off and all the boost pressure will go to the bottom port while the top port will be vented to the atmosphere – same as before. But at maximum boost pressure both will be on so the bottom port of the wastegate will be vented to the atmosphere and not seeing any boost, while the top port will see all of the boost! That better than the previous option but what is even better is that by controlling the two solenoids in stages we can achieve a lot more resolution and precision!
How can we do that easily with the LDperformance electronic boost controller?
Simply connect the second solenoid (the one connected to the wastegate top port) to the boost controller like this:
The boost controller will automatically detect a second solenoid and will allow setting Duty up to 200. So basically it works in exactly the same way as before when using duty 0-100% but now duty can be increased up to 200 where the second solenoid starts working. As simple as that. All additional settings for example Boost by RPM or Boost Target will keep working and allow duty up to 200.