Help Understand GTT Boost Setup

[DraftySquash]

Hi everyone,

Apologies in advance if this feels like a topic covered multiple times. I'm only asking because some of the old topics I found are missing images now.

I'm in the process of getting a manual boost controller (BC). Nothing fancy, just getting a manual one for now as I don't plan to go crazy with it and would not go over 10 PSI. My car is not jacked up on boost steroids to do crazy numbers.

I want to understand the OEM setup of the boost solenoid and vacuum lines on the R34 GTT so I know what needs to be changed when I do install the BC. I sketched the current setup to the best I could see and it's on the diagram attached.



If the boost controller 'Wastegate Arrow' goes from nipple 1 to 2. My understanding is that the red vacuum line's "F" connector-end should be connected to BC nipple #2?
Nipple #1 is meant to have the "pressure source" so what vacuum line would that be? Is it the green vacuum line? 

From what I have read here, the OEM boost solenoid is not used at this point. So that can come out and then I can just plug the nipple that usually connects to the blue vacuum line? 

So would the final setup look something like this?

 

Thanks in advance. I don't want to already be knee-deep into pulling out vacuum lines before understanding this. I'm a noob when it comes to boost setups so trying to learn as I go.

[GTSBoy]

The stock boost solenoid is just a valve. Power it and it is open. Unpowered, it is closed.

When it is closed, there is no boost bleed out through the solenoid back to the inlet. The wastegate sees all the boost pressure, thus you get the wastegate's spring pressure as your boost pressure. 5 psi.

When it is open, it lets some boost escape. This causes the static (boost) pressure in the line to the wastegate to be lower than the pressure in the intercooler pipe. There is probably a small restrictor in the solenoid or one of its lines to limit the flow rate of the escaping air, which limits how far the static pressure can fall, which limits the extra boost. The boost has to climb above the original/wastegate setpoint until the wastegate sees 5 psi. You get 7 psi in the intercooler pipework.

A manual boost controller is exactly the same setup, just without the ability to change it on-off. It's always set to whatever you set it to. There is a small leak from the boost controller. The more you screw the adjuster in, the more it leaks, the lower the pressure seen at the wastegate and the higher the boost will be.

So, yes, your diagrams are correct.

[DraftySquash]

@GTSBoy that’s good information and thanks for sharing that. 
I’ve read the GTT has 2 stages of boost? 5psi or so at lower RPMs and then 7psi. 
So I assume, with a boost controller it will be one standard pressure. I got no issue with that until I invest in an electronic boost controller.

With the setup after the boost controller, should I still keep the solenoid plugged in to power? Just so the ECU is happy? Or does unplugging it and completely removing it cause no issues? 

I’ve got myself booked in for a Nistune install and tune next Monday so pretty excited 😝 

[GTSBoy]

The ECU doesn't care if the solenoid isn't there. There's no sensing/feedback from the solenoid. The ECU just gives it power, or not.

Make sure that you Nistune tuner knows damn well how to tune a Neo. They suck. You have to take a lot of care to override bullshit to do with the boost sensor and a few other things to stop them being a dick.

[Milkmun]

Who's doing your Nistune install and tune? 

Could always ask them to install the MBC.

[DraftySquash]

On 11/2/2025 at 9:51 PM, Milkmun said:

Who's doing your Nistune install and tune? 

Could always ask them to install the MBC.

It’s Shane at CMS performance doing the tune. 
 

CMS performance was the only place in VIC I could find that would supply, install and tune (and had good feedback)

Yeah that might be a good idea 😂

Less chances of fkn it up 

Edited 5 hours ago by DraftySquash

[Milkmun]

On 11/02/2025 at 10:04 PM, DraftySquash said:

It’s Shane at CMS performance doing the tune. 
 

CMS performance was the only place in VIC I could find that would supply, install and tune (and had good feedback)

Yeah that might be a good idea 😂

Less chances of fkn it up 

Big drive from the west to Seaford. Good luck man, let us know how it all goes.

[DraftySquash]

On 11/2/2025 at 10:15 PM, Milkmun said:

Big drive from the west to Seaford. Good luck man, let us know how it all goes.

lol I know!!

I’m actually staying over at a mate’s place in SE the night before. 
not because I don’t like the long drive. I just don’t want to drive from West to Seaford around 8am on a Monday 😂

traffic would be wild. 
 

The Skyline actually does the West to SE trip without issues. My family is on that side. 

[DraftySquash]

I think a 60-90 mins drive is worth it, if the mechanic is good and has experience. 
that’s what I’ve heard about CMS, so I’ll let you know how I go after Monday