Updated for 2013. Way back when, I colored in a vacuum/wastegate diagram of an RB26 engine for the Nissan Skyline GT_R. As far as 1980s-1990's engines go, the RB26 is pretty simple. Still there are a few vacuum lines that get people confused. This causes either minimum or maximum boost, so its a good idea to check everything out. Also under the collector is a bit of a tough place to work, so a leak may never be noticed.
|JUN collector with Q45 throttle body. Stock collector. The smallest rear fitting is for boost source|
The boost supply to the factory wastegate solenoid comes from the back of the plenum/collector. The last nipple under the plenum supplies the wastegate solenoid, and directly to the wastegate actuators.
Boost pressure presses on the wastegate actuators to open them, against base spring pressure.
|RB26 bolt on turbochargers|
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.
|Fuse box, factory boost solenoid, and battery|
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. If you plan on running more than about 14 psi on the stock turbos, have a spare set on standby.
|Rear of balance tube. This gives you a nice stable vacuum/boost signal. We normally pull the tube, drill and tap it|
|Tapping rear of balance tube|
|Rear of balance tube drilled and AN fitting put in. We use this to run to boost sensor.|