R34 Rb25 Na Inlet To Plenum "y" Shaped ?

[discopotato03]

Hi all , I was looking at a section of an R34 engine manual and I noticed that it mentioned the "Y" shaped gadget for the inlet on RB20 and RB25DE engines .

It makes me wonder if this would work better distribution wise on an RB25DET . How common are the bolt patterns between R33 and R34 RB25's - between the upper and lower halves of the inlet manifold ?

Also is the idle bypass housing the same ?

Cheers A .

[Dale FZ1]

Worth pondering, but if it worked better for forced aspiration I suspect Nissan's engineers would have incorporated it into the Neo DET as well as the DE.

[666DAN]

For the N/A it's to do with the variable inlet, there is a butterfly valve that sits inside the plenum and opens up at around 4700rpm. Basically each lot of 3 cylinders is fed seperately under low to mid range, then for top end they open up. If you disable this butterfly the car has virtually no top-end. It's pretty interesting to see that just opening up the plenum has that effect.

Something to note though, when I boosted my 25GT it was at the point the plenum opened up that there was some serious power, I didn't actually think of leaving it open full time til I didn't have the car anymore.

[discopotato03]

I was under the impression that R34 RB25's had a second "fly by wire butterfy" to do the traction control thing - sort of pre purely ECU conrtolled throttle .

I had wondered if Nissan were struggling to get enough grunt to keep people happy with N/A variants of the R34 so were trying to get their inlet manifolds to flow a bit better .

What I'm thinking about is the possibility of using the "Twin Inlet" plemum top on a turbo engine to get a bit better air distribution than a single "hole" to feed 6 cylinders . I had wondered if the chamber was divided into two and seperate throttles used how much better it would be .

Cheers A .

[666DAN]

The GTt has traction control yes, the 25GT doesn't.

As I mentioned the 25GT engine has the split chamber, opened by a signal from the ECU (same pin as the boost solenoid signal in a GTt) The twin inlet would probably work very well, if you remove the butterfly valve as it would be more of a hinderance under boost.

The manifold will bolt up, but there would be a fair bit of effort re-running hoses to the AAC valve etc etc, may be worth it though. Circled in red is the valve that seperates the two halves of the pleum

[crack]

i thought about this a while ago to the point that i drew up a basic "Y" pipe. i thought a twin trottle setup would be the go hence the bead at the manifold end. but if going single you would obviosly delete the beads and weld straight to the manifold.

[DatsunBanana]

Sorry for reviving an old thread but it's one of a few places other people searching this subject might end up.

I've done a +t on my R34 using a GTT ECU. The butterfly valve in the NA plenum is open when there's no vacuum - i.e. default position under spring pressure. It closes the chamber when vacuum is applied to its actuator from the solenoid valve.

Page EC-44 of the R34 manual suggests that pin 104 on the NA goes to ground at idle which makes sense as that will open the solenoid and provide vacuum to the actuator to close the plenum for torque at low/mid rpm. Same page also suggests that the GTT ECU pin 104 gives the opposite signal while at idle meaning that when used on an NA it would keep the butterfly open at low/mid RPM.

The manual shows that on the NA ECU it changes the state of pin 104 at 3500 RPM to close the solenoid valve which would remove vacuum from the actuator and let the butterfly reopen under spring pressure for high RPM torque. Interestingly the manual doesn't mention the 4700 RPM figure but just mentions the GTT ECU will ground pin 104 when the engine is raced suddenly :-)

So with pin 104 working properly what I'd get is the opposite of what I'd want ... plenum open at low revs and closed at high revs. However my ECU pin 104 isn't grounding at high RPM anyway for some reason. I wonder if that could be due to the error code for the missing boost pressure sensor. I plan to trick the ECU anyway with some diodes so might find out if that makes a difference.

Anyway for now my thinking is that all I need to do to keep the plenum open all the time is disconnect the solenoid plug which is what I've done. Alternatively I could just use the plenum vacuum for something else instead of running it to the vacuum canister / butterfly actuator.

Any comments on agreement or different understanding is welcome as this is what I've figured out from reading up online and in the manual and from checking the signals I'm actually getting.

I also wondered about this ... if I connect the plenum vacuum line direct to the butterfly actuator it will pull the butterfly closed. What will happen when the car hits boost? Will the actuator get positive pressure and push the butterfly open again? Is that a crude approximation of what the solenoid accomplishes or is it a stupid idea? :-)

There's a related thread here with a bit more info about the solenoid ... https://www.sau.com.au/forums/topic/271853-midrange-flat-spot/

Phil.

[Aiden.owop]

I'm doing a turbo conversion on my r34 20de neo currently and doing some research on what these valves do, does anyone know what the system is on the inner intake manifold where the injectors seat, there's another solenoid. 

Back to the butterfly in the plenum, I applied pressure to it using a compressor and it doesn't lean and just pushes the butterfly "more open", I'm thinking of trying when I've got the motor back in and comes tuning time if I hooked the actuator up to the manifold so the butterfly closes under idle and when your put of boost aka highway driving and low throttle driving then once you go into boost the butterfly will open but I'm not sure if it will open too early but I suppose boost won't come on till around 3-3.5k rpm anyway. 

[GTSBoy]

Well, if there is a mechanical stop involved in the butterfly's linkage, then it simply cannot open more than fully open, even with boost applied to the diaphragm. So....just let boost go to the diaphragm, have it do nothing (because of previous sentence), and not worry about it?

Worst case, you draw up a plan for using a check valve or two to block boost from being fed to the diaphragm and somehow ensure that check valve doesn't leave a vacuum signal trapped in there when you don't want it. I strongly suspect that this would end up being too difficult to do simply (ie, doable, but with a lot of extra check valves and possibly solenoids added in), and probably not worth the pain, given the first idea above, anyway.

[Neostead2000]

I believe Nissan may have also done a technical explanation/write up on their own version of this, but Toyota have the EXACT same systems on some of their equivalent motors, both the "torque valve" in the center of the Y-pipe and the "swirl valves" just before the head ports. Here are some brief infos about it, taken a re-quote from the Toyoda forums:

------------------------------------------------------------------------------------------------------

---Theory----
Using laws of inertia, thermodynamics and physics the toyota engineers discovered that the opening and closing of the intake valves creates acoustic energy pulses that bounce around inside the intake manifold and chamber. They then developed a system, called ACIS, to control and manipulate those acoustic pulses to create a "supercharging" effect.

By varying the length of the intake runners through the use of valves, the toyota engineers found a way to time the acoustic pulses so they enter the cylinders through the intake valves. This means that after an intake valve closes and creates this acoustic pulse, the pulse bounces off the intake runner and chamber and then is timed to enter at the next intake cycle so the valve is opened with a pressurized acoustic wave being forced into the cylinder.


---Application---
Toyota has many NA engines that utilize the ACIS system. (7m-ge, 2jz-ge, 2jz-fe, 1mz-fe, ect, ect) In our case, the 7mge, there is a butterfly valve (intake air control valve(IAC)) placed in the middle of our intake manifold behind the union of the Y-pipe. This valve is controlled by an ACIS actuator. The Actuator is controlled via vacuum provided by the either the throttle, VSV's or the ECM ( or all three). There is a vacuum storage tank located beneath the intake manifold and that is connected to a port near the Intake air control valve.


---Operation---
I'm not sure on the switchover throttle position for the 7mge, but the activation RPM is 4200. Before that point at WOT, the Air control valve is closed, meaning that the cylinders are getting shared air from just behind the throttle body. This means that the engine is utilizing long intake runners. Under WOT, past 4200 rpms, the air control valve is opened and the cylinders are now getting shared air from the center of the intake manifold, meaning the engine now has shortened intake runners. ( see diagram on site)

On the 2JZ-FE engine, there is an activation rpm of 4,500 and a 30% throttle crossover map. meaning....

low throttle... ( less than 30%)
<4500 rpm = valve open ( short runners )
>4500 rpm = valve close ( long runners )

high throttle... ( more than 30%)
<4500 rpm = valve close ( long runners )
>4500 rpm = valve open (short runners )

This system ( two stage acis) essentially gives you two torque curves. The valve is timed to open on the downfall after the first peak, so the engine has potential to make equal or more power later on throught the power band.


--- Modification ---
Modifying the ACIS system is not recommended because it has been tuned for the specific engine. But the thought does provoke interest. If by changing the activation RPM and/or throttle %, could you tune where you want your torque to peak?

I have the ACIS system on my now turbocharged 7M-GE and remarkebly it has still provided two torque curves between the designated 4200rpm. I plan to do some experimentation with ACIS during my next trip to the dyno. I will perform runs with the valve closed ( long runners), with the valve open ( short) and then multiple runs using different activation RPMS. If this system can yield more power because of its changing attributes, then it may be a desired modification for mid-power performance enthusiasts.
 

----------------------------------------------------------------------------------------------

My thoughts:

It is very possible that the engineers decided to not use these systems on their turbocharged versions due to diminishing returns, meaning the increased airflow and airspeed from the forced induction is outweighing the benefit of these valves so they completely removed them to simplify the overall package and less airflow disturbance inside the runners. That said, it's not a clear-cut answer and we have to remember that the OEMs first and foremost prioritize cost and reliability. If they didn't, then we'd be looking at mass market cars which are pretty much F1 track cars worth millions :).

 

Interestingly most modern engines especially from the VAG group do in fact use those same valve systems in their GDI and diesel engines, which all come turbocharged from the factory. They simply have gone more in-depth and figured out a way to make the systems be effective both under low-RPM low-load conditions as well as once the engine is fully charged. Meaning, these are not snake oil or gimmick systems they once implemented. This stuff works. The good thing in our case is that Nissan, Toyota and Mitsubishi have given us the switchover points/values for when these valves open and close, and with modern aftermarket ECUs we are more than capable of fully reconfiguring when they start to work and how.

 

Personally I am also doing an RB20DE +T and will initially run the stock intake plenum and Y pipe. I will compare how the car performs with the systems active with stock values, deactivated completely and then configured to open/close at different RPMs and throttle positions. Simulating long intake runners increases air  velocity, which in turn can increase the rate at which exhaust exits the head and flows into the turbocharger, which in turn would have an effect on spool-up.

 

[DatsunBanana]

12 hours ago, Aiden.owop said:

I'm doing a turbo conversion on my r34 20de neo currently and doing some research on what these valves do, does anyone know what the system is on the inner intake manifold where the injectors seat, there's another solenoid. 

Back to the butterfly in the plenum, I applied pressure to it using a compressor and it doesn't lean and just pushes the butterfly "more open", I'm thinking of trying when I've got the motor back in and comes tuning time if I hooked the actuator up to the manifold so the butterfly closes under idle and when your put of boost aka highway driving and low throttle driving then once you go into boost the butterfly will open but I'm not sure if it will open too early but I suppose boost won't come on till around 3-3.5k rpm anyway. 

You may have already seen it but there's been a bit more discussion on this and the other valves (swirl valves) in the NA RB20 and 25 NEO differences thread in the Naturally Aspirated Performance forum. When I posted above I was still trying to decide what to do. I've been running 5 years now with the hose just disconnected from the diaphragm and all runs really well. You've got me thinking again about trying to connect a boost/vacuum line from the plenum now to see if there's any noticeable difference.