2 stage boost on R34 - please prove me wrong

[DatsunBanana]

2 stage boost on R34 - please prove me wrong

This is really bugging me since I did a NEO +t conversion and used a GTT ECU. Nearly every discussion says there is 2 stage boost on an R34 - that over XXXX rpm the solenoid bleeds off some air and gives higher boost. That is except a few posts out there saying that the boost solenoid is always bleeding under normal operation and only closes in limp mode and reverts to actuator pressure.

There's been some discussion with the +t guys that the pin 104 signal from GTT ECU can do a similar job to pin 104 on the GT ECU which controls the plenum butterfly valve on the NA engine.

The R34 service manual clearly explains the way pin 104 works for the GT - it turns the solenoid on at idle and off above 3500 rpm. But all it says for GTT pin 104 is that it's off at idle and at approx 2000 rpm it comes on when the engine is suddenly raced. Where is it documented apart from hearsay that it switches at over XXXX rpm for the GTT?

To satisfy my curiosity I went out for a drive with a voltmeter connected across the solenoid plug from pin 104. Under any acceleration ("engine raced") the voltmeter showed a steady voltage (solenoid open). As soon as I relaxed the throttle the voltage dropped to zero (solenoid closed). I took it right through the rev range and as long as it was above 2000 rpm and accelerating the voltage never changed at 4500, 4700, 3500 or any other rpm. If I relaxed the throttle at 5 or 6 K rpm then the voltage dropped back to zero - it didn't maintain the 'solenoid on' voltage even at those high revs.

So what I saw seems to agree with the service manual. But where is the idea of two stage boost coming from, I just can't see how it would work on the basis of what the manual says and what I saw in my test.

I hope I'm wrong and can have it explained why so I can try using pin 104 to control the butterfly valve.

[Dose Pipe Sutututu]

Nistune

[GTSBoy]

Of course it's a boost control.  Of course it's not "2-stage boost".

The factory actuator gives 5 psi.  When the bleeder solenoid valve is switched by the ECU, you get 7 psi.  The ECU does this when the ECU wants.....but in general, it has nothing to do with RPM.  It is nothing like the actuation of the plenum butterfly.  It is primarily intended to give lower boost in 1st gear.  I wouldn't be surprised if the ECU also drops the boost when it is doing traction control, but I have no evidence of that....just seems logical.

[DatsunBanana]

Thanks. I fully expected replies from people saying that their gauges are clearly showing that there are two stages of boost and that I'm completely wrong. There are so many posts on different forums about grounding a pin to keep the boost high so what's all that about? From what you've explained that's a waste of time if the system is already at high boost except under certain conditions.

Is the R33 different and is that causing confusion with people?

[Dose Pipe Sutututu]

Get your ECU Nistuned, use the 3D map to control your boost win.

[GTSBoy]

1 hour ago, DatsunBanana said:

Is the R33 different and is that causing confusion with people?

Nope.  Same same.  Except for the possibility of small differences like maybe traction control interaction, because R33 had no TC.

Johnny's right about being able to control boost from Nistune, but he's missed the point that you want to use the boost control output to run your plenum valve.  However, there are intriguing possibilities to do as he says and use the output to try to run your valve, with the 3D table he talks about.  It's just that....it may work, or it may be a pain in the arse.

[Kinkstaah]

5 hours ago, DatsunBanana said:

? From what you've explained that's a waste of time if the system is already at high boost except under certain conditions.

Is the R33 different and is that causing confusion with people?

It's to make sure it's under high boost under all conditions all of the time. Certain conditions from Nissan are very conservative for a person who wants more power at the cost of a paperclip

[DatsunBanana]

Very interesting - at least all that makes sense and will stop it bugging me. Thanks for the info fellas.

[Dose Pipe Sutututu]

If you need Nistune boards or a Nistune board fitted I can organise them for a good price. Also have the ECU bench tested and loaded with a base map with whatever injectors and afm mix you have so your car is driveable to your favourite tuner.

[DatsunBanana]

Thanks Johnny although I'm in the UK. (I really need to add my location to my sig). I'm sure I will at some point go for decent engine management.