Prepping the RB26 for SDS

[Zhadman]

Yesterday I began stripping down my '26 to prepare it for paint and the eventual installation of an SDS EM-6F system. While the SDS installation as a whole should be fairly straight forward I have some questions regarding the removal of stuff ( ) from the engine.

 

I'll start with the Intake Side:

 

Here is my understanding of the system (the terminology comes from an Australian FSM):

 

Air is taken from the Collector (intake) and fed to the AAC Valve (Auxillary Air Control) which is controlled by a signal (AAC valve control solenoid valve signal) from the ECU. When the Valve is not controlled (un-plugged) it should be 'closed' and should allow the motor to sustain a consistent 900rpm idle.

 

The AAC feeds a connected Air Chamber. In addition to this, air is also input into the Air Chamber from an 'Air Regulator' (which also pulls air from the Collector).

 

This Air Chamber feeds the Balance Tube which is connected to the intake manifold (the part between the head and throttle chambers).

 

I am assuming that the Balance Tube injects air after the Throttle chambers to accomodate the idle. (I'll inspect my Intake Manifold and Balance Tube later to confirm).

 

 

The Throttle Chambers also have 'Supplemental Air Paths" which appear to provide a means for air to bypass the throttle plates:

 

 

Now... I know the SDS has a 'Fast Idle' solenoid option to allow air to bypass the throttle plates. I am assuming this option is unnecessary because the AACV, even when uncontrolled, will allow the motor to idle.

 

What role/function does the Air Regulator provide? Does it remain installed? I don't really see any reason to remove it so I'm just going to leave it in place.

 

On the hot side:

 

My motor did not come with the Turbocharged Pressure Control Solenoid (boost controller). Can I eliminate the hard/soft piping that ran to this unit or will they need to be retained for use in the SDS system? There is quite a bit of plumbing there that appears to be unnecessary.

 

If these lines ARE removed what controls the wastegate actuation/control?

 

The 6F has a 'Boost Limiting' Feature but It doesn't sound like a direct replacement for a boost controller. Is an MBC or EBC used in conjunction with the SDS?

[cheftrd]

The air regulator is thermostaticly controlled. It increases and decreases air as the engine temp fluctuates (it's bolted directly to the engine coolant outlet). It does not require the electrical hook up to work properly. The AAC valve can be controled by the SDS for warm-up idle up and air conditioner idle up (if used).

 

The stock boost control valve must be removed whenever boosting the RB. Otherwise, the boost will be very erratic. You can use the stock metal actuator feed tube coming around the back of the head. Hook this up to one of the two small air outlets (6mm) on the front side of the air chamber. If you are using a boost controller, use one of these ports for the feed and run the outlet to the actuators. The SDS does not control boost, it has a limiter to keep the engine from over boosting.

[Zhadman]

Thanks Matt!

I didn't know that the AAC could be controlled via the SDS. I know that I want my warm-up idle to be greater than 900-950rpm (which is what it would be if the AAC was not controlled).

 

The air regulator supplements the air fed to the air chamber by the AAC valve. that makes sense. The more air... the more the idle rpm. Knowing this... is it even necessary to control the AAC with the SDS? Without control, on a warm engine, the AAC will (should) maintain a standard 900-950rpm idle. When cold the air regulator will add supplementary air to increase idle for warm-up, right? I know I'm getting into theory of operation here, but it's interesting none-the-less (well... to me! )

 

Keith

[Guest JAMIE T]

Interesting stuff... I bought Stony's set-up which is already wired for the SDS, but I don't have any diagrams or instructions for it. So, I don't know how to tune it. Also, I was hoping to get rid of all that ugly stuff under the intake manifold. So, from what you guys are saying, I need that stuff?

[Zhadman]

Yep... looks like it's all crucial to controlling the idle.

Although it should be relatively hidden beneath the Collector I suppose you could relocate it. But would longer hoses (with an increased volume of air between the AAC and Balance Tube) affect operation much? Is the Air Chamber, Balance Tube, and associated plumbing designed for a specific volume? Hmmm....

 

I was bouncing around, in my head, the idea of fabricating a light gauge sheet metal 'shield', utilizing the Air Chamber mount locations, to hide it.

 

All the recommendations I've recieved (from those who have built up these motors) is that it should remain.

 

Jamie - Your motor came wired for SDS or came with the SDS system already installed?

 

---EDIT ---

I just re-read Stony's old ad. It said it came with the SDS system fully integrated.

[Guest JAMIE T]

Sooooo, What about the guys who have fabricated manifolds and single throttle bodies like Joel's?

[Zhadman]

That, sir, is a good question!

 

I took a quick look at Joel's intake (kinda hard to seein his photos) and he's still using the stock manifold between the head and intake mani (collector...to keep with my previous terminology ).

 

Technically he can still use the stock Air Regulator and AAC valve to control idle since idle air is injected into the manifold after the throttle plate(s).

 

[cheftrd]

The Nissan system does not have an idle air control motor like more complex Toyota systems. First, the PVC valve in the balance tube (hose comes from the cam cover) must not be blocked. This feeds air to the balance tube at idle. The idle speed can be adjusted with the idle screw in the air chamber.

 

The air regulator valve will only provide minor corrections. If you are running large injectors or whatever, It's going to be hard to get the fuel trim just right so that the engine doesn't stall when it's cold. To cure this, use a relay to run the AAC valve. The relay is actuated by the SDS grounding the field coil of the relay. You can also use a diode and run a wire from the AC compressor clutch to the AAC valve itself. This will idle up the engine when the AC comes on. This is the original purpose of the AAC valve. The diode in the wire from the compressor clutch keeps the compressor from turning on when power is supplied to the AAC valve by the warm up circuit. The engine may idle as high as 1500rpm. BEWARE with big cams!!! If the AC is running and the valve is on, you will lose substantial brake boost due to lack of vacuum. The AAC manifold that bolts to the air chamber is a direct swap for the one from the Z32 VG30DETT. The Z has two solenoids, one small and one large. I use the small one for the AC and the large one for the warm up. No problems with 272's. The RB26 AAC manifold can also be adjusted for the amount of air bypass, but you have to remove the putty closing the adjusting screw. You will probably break it attempting this operation.

 

On race engines with custom surge tanks, manifolds, etc, the air chamber can be mounted remotely, or you have to design your own air bypass for idle and idle up. I use a fixed size orifice in a hose from the piping to the plenum in a single throttle or the balance tube in the six throttle configuration. Then add an adjustable valve for idle control, and finally an electrically operated, adjustable valve for warm up.

 

Here is a really good tip that will save your motor: When using a large, single throttle like the Q45, etc, never adjust the idle with the throttle!! That little screw on the side is a throttle stop, not an idle adjustment. It's meant to keep the butterfly from wedging closed. If the butterfly does not touch the bore of the throttle body because it's open to accommodate additional air for idle, it will flex the throttle shaft severly when you close the throttle under boost. Vacuum on one side and a boost spike on the other will try to close the butterfly. The shaft will fail at the weakest point (butterfly bolts) in short order. Best case is that your engine eats a bolt. I've seen this happen alot.