After the 100th time of reading someones post on what vacuum lines went where on the RB26DETT as used in the Nissan Skyline GTR, I used Paint(not a graphic artist), and colored in a drawing of the vacuum/boost diagram for the RB26. Hopefully it might help you out.
Boost pressure presses on the wastegate actuators to open them, against base spring pressure.
|Stock boost solenoid.|
The way that boost is raised is by venting some of this pressure back to the inlet side of the rear turbo. The more pressure bled off, the higher the boost pressure will be.
The factory solenoid line has a restrictor in it. The restrictor is marked by a yellow ring on the boost line. This restrictor limits the amount of bleed off from the wastegate solenoid. The more pressure you bleed , the higher your boost pressure.
Do you see where this is going ?
The problem with the stock boost control setup is the stock turbos. If you run the boost pressure too high, you will lose a ceramic exhaust wheel. Normally aspirated Skyline GT-R's - ones that lose a turbocharger exhaust wheel- are slow.
|The ceramic exhaust wheels are light, but fragile|
If you add a restrictor to the small line under the plenum/collector, the one that supplies the wastegates, depending on the size of the restrictor you can run a lot of boost. With our setup a 1.0 mm restrictor will gave us about 24 psi of boost.