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Sunday, July 15, 2007

Nissan Skyline GT-R RB26 vacuum wastegate diagram

Edit- This is correct. The lines go from high to low behind the engine

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.

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.

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.

17 comments:

trouble maker said...

this seems to be the only information to cover the vacuum system on the GTR R32 , it is wrong !! , the blue and green have been coloured in wrong , goes from actuators in green switches to blue - back to green the back to blue , confusing !

Sean Morris said...

You didn't read the words. Ther are two separate lines stacked on top of each other. They don't show in the diagram, but they are there. So the color doesn't change, rather what the diagram shows does.

Trust me, the diagram is right.

trouble maker said...

Read it , studied it , blew up the picture ! , not here to argue , but , if you look closely the green pipes from the actuators , it is the the top pipe ( of 3 pipes , 2 air pipes and 1 water pipe ) but it is marked blue after the turn at the rear of the engine , it then turns back to green after it goes under plenum and takes the lower position of the now 2 air pipes , it then emerges as the blue 1 with the restrictor . When trying to sort this out for real on my car it got confusing because of the change in colours in the diagram do not match in the car . I have put the restrictor from the solenoid pipe into the boost source pipe , as suggested above in script . So as I say not here for a fight just the colour confusion threw me out !

Sean Morris said...

You know what I colored it in without an engine in front of me, and I think you are correct. I did spend a little time doing it. Looking at it close, I think I swapped them back and forth. Let me find the original file, and a engine, and double check it.

Anonymous said...

Hello mr. Sean! I checking out your diagram especially the restrictor part. I then checked my hose with yellow band, and to my surprise it still has something hard inside thesaid hose. Not the first owner of the car by the way. But I noticed with the Greddy EBC off, I was already at around 0.85 bar of boost and that is not fully tested yet at wide roads on WOT. I'm sure this GTR has an aftermarket ecu by the way. So my questions are;
Is the aftermarket ecu the one responsible for the nice boosting?
Can the ecu even do that with the round restrictor even on it?!
And isn't it when you install an EBC you are required to remove the restrictor?
My ebc is profec B spec 2 by the way, and I don't know why the Jap owner did not remove the restrictor. Thanks in advance R guru!

Sean Morris said...

The restrictor limits the amount of bleed off. If you change the solenoid, or change the routing of the lines, then things will change. To take the number of variables out of the equation, its best to remove the restrictor, and set boost from there, rather than with the restrictor.

Some people don't know about it.

0.85 is about stock boost pressure, can you get more than stock?

Anonymous said...

0.85 bar is stock boost?? I read in forums that it was only round 10 psi or 0.68 bar? Confused a bit now.

Ah so it is better with the restrictor off. Ok then. Some people and tuners though say it is "risky" and recommends just drilling out hole of the restrictor.

And Sean, can aftermarket ecu set the boost to 1 bar even w/o the help of an EBC and w/ the restrictor still in place?

Sean Morris said...

An R32 will see peak about 0.80(11 psi), an R33 will see about 0.85(12 psi). R34 is about 1 bar peak.

The boost control system in the GT-R is dumb. It doesn't really set anything. No feedback, the ECU doesn't see boost at all.

Sean Morris said...

So I finally checked out a set of hardlines, and yes the lines go from top to bottom, aka switch positions. The original colors are correct. See the pictures of the real parts for more clarification.

Anonymous said...

Hey Sean can I just replace the hose with yellow band (restrictor inside) with a new silicone hose? So I can place it back if I want stock boost, and of course to save the hassle of brass plumbing. :)

Another thing mate, since I'm a new owner, I have not yet tuned my boost controller so it is still "off". But the boost control vacuum lines were already set up properly. So with that scenario, will the benefit of the boost restrictor removal still take effect?

Last but not the least, I heard some say to by pass the oem boost solenoid valve (pcm valve) as well together w/ the restrictor removal to have the boost gain. True or just hearsay?

Sean Morris said...

You can replace the line with the yellow band, with a regular hose. Its purpose is to limit the amount of bleed off. Once you can bleed off more you raise boost.

If you have an aftermarket boost controller, then all bets are off. Its hard to say what it will, or might do.

It all depends on what I am using for boost control. You don't need the stock solenoid.

Anonymous said...

My understanding was if the boost controller (greddy profec one) was off it will be back to oem factory boost.

But basically the PCM is not needed if there is a boost controller, but the lay out of the Greddy ones does not instruct it to be by passed.

Last one, what is the function of the PCM Valve's small socket plug? Is that the one that reads boost for the factory gauge or for ecu?

Sean Morris said...

You don't need the PCM/wastegate solenoid. I prefer to remove it if I use an aftermarket boost control scheme, but then I run all new hoses. If I have the collector off, I drill and tap it for -4 AN. AN fittings on the solenoid. Less failures that way.

PCM valve small socket. Its just two wire. Just solenoid control.

The sensor on the firewall, that is connected to the back of the vacuum tube on the rear of the engine, only drives the gauge. The ECU does not see boost at all.

Sean Morris said...

Picture updated for 2013. http://www.gtrusablog.com/2013/02/rb26dett-vacuum-and-wastegate-diagram.html

StarmexX said...

Hey Hey! Urgent HELP! Car run out of water and overheated! I noticed A pipe or hose has a small leak and the water slowly comes out when the pressure builds, the pipe that has the small hole is near the back of the motor which it is visible from the top, just under the windscreen, just to give you an idea of where it is. I think it's a turbo pipe and would like to know how long are the pipes? The mechanic has told me not to drive the car as it might ruin the turbo... Lachella@hotmail.com if anyone can help I much appreciate it! Grace :)

Sean Morris said...

Its hard to say what is leaking. You have to get back there to investigate it. On the back of the engine are the heater hoses, plus water lines to the turbos. The heater lines are bigger, turbo lines are smaller.

How hot did the engine get? Do a leak down test,make sure you didn't hurt anything.

Other than that, just find the leak, repair it, and test.

trouble maker said...

had the small pipe on mine explode and cause same thing , replace pipe and run as it is only way to tell if all ok . It is a pain of a job , but i think pipe is straight - so no hunting for an original molded curved pipe ! try finding a mirror to see what is going on , or give to a mechanic = it is just a pipe that needs replacing . It sounds like time to check all rubber pipes on engine as they will all get old and suffer .

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