DatsunBanana

Nice! That makes perfect sense now - thanks 👍

Couldn't quite see what you mean from your photos, can you share a pic of the drilled hole and spacer? Still promising myself that one day I'll fit all the manual bits I've got in the garage. Is the rusty one the R33 pedal?

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.

That 'pump' is a vacuum tank, I guess just a reservoir for holding the vacuum. On the 20DE looks like it's used for both the swirl and torque butterflies. One line is to the plenum and the other two will go to your torque valve solenoid and swirl solenoid. The solenoids will have their own lines to the actuators. The solenoids seem to switch the actuator hose to either the vacuum tank or the air filter side of the throttle body. This is from page EC-3 in the manual. On 25DE the tank is just for the torque valve so I binned that and the solenoid and related hoses and used the old tank take-off for my boost gauge I think. From experience I know the torque valve is under spring pressure keeping it in the default open position. I don't know about the swirl valves but if they are sprung to open position then removing the vacuum tank, solenoid and hoses from the actuator would (I'm guessing here) let them spring quite firmly open (??) Page EC-44 in the manual gives info on the RPM threshold for the solenoid ON/OFF signal.

The main torque valve shouldn't need hacking as it defaults to open without the vacuum pipe connected (at least on the 25DE). Not sure about the swirl valves but in your pic they look open by default. On the 25DE I used a GTT ECU but it doesn't have the signal to control the valve. Other discussions seem to suggest at boost the valves won't do much but would still be cool to know what it's like controlled by an aftermarket ECU.

Have you tried Conceptua tuning on eBay? They have a few options for 33 gtst. Great to deal with too.

I was always of the same opinion as Kinkstaah that using a GTT auto ECU would be complicated. If you've got the R34 service manual, pages EC11/12 show that GT auto and manual have the same ECU wiring that uses a separate transmission control unit and the GTT auto has the transmission control built in to it. Page AT3 states that plainly. As per the diagrams, wiring for manual GTT ECU is same as GT auto/manual so that's what I used on my auto NA+t. It works fine and just uses the original GT transmission control unit to look after the auto box. As mentioned above, popular opinion is that there could be problems if the transmission circuit inside the GTT auto ECU creates conflict or doesn't talk with the GT transmission control unit still in the car. Pages EC13/14 will show you which pins are different and what they control. On page EC11, pin 79 of a GTT auto ECU (multiplex communication) is shown as only being for TCS/ABS but on page EC12 for non-turbo it also goes to the separate GT TCU. Pages AT8/9 have the transmission circuit diagrams (top right corner on page AT9 shows the connections from separate TCU to ECU). If you're gonna give it a go, those refs might help and if you get it working report back to feed the knowledge base. R34Nur posted a couple of weeks ago and said it worked fine with auto GTT ECU but that does go against popular opinion.

When I did this few years back I read everything I could find on the subject including the thread here for example: I was happy to give it a go based on Dan666's experience but only after I checked out EC-11,12,13,14 and AT-8,9 in the workshop manual for myself. As I understand it, the required signals will still be connected between the manual GTT ECU and the existing separate TCU via the GT loom (e.g. pin 29 speed signal and pin 37 throttle opening signal). I'd suggest to anyone planning this swap to look at those pages and get an idea of the similarities and differences. Apart from that I can only speak from experience - I swapped in the manual GTT ECU and it's been fine on my NA+t. I said 'almost' plug and play because there will be errors related to traction control and boost sensor which aren't physically there on a GT. But those were easy enough to workaround - I fed suitable voltages to the correct pins on the ECU via diodes to stop the check engine light coming on. Pin 104 signal has different purposes between GT/GTT ECUs so a GTT ECU won't control the GT inlet manifold valve if that's still fitted. Little bit of info on page EC-44 for anyone interested. The signals for A/T position indicator dash lights are not present on the manual GT ECU. Mine never worked before I did the conversion so I can't say for sure what will happen to those but I don't see why they wouldn't get the signals from the existing GT TCU. Pin 79 is an interesting one. Looking at page EC-18, that signal relates to malfunction detection. For GTT it relates to TCS/ABS e.g. 'Malfunction (open/short circuit, etc.) is detected in multiplex communication line between engine and TCS/ABS'. And for GT it's different: Malfunction (open circuit, short circuit, etc.) is detected in multiplex communication line between ECM and TCM. [RB25DE). That difference hasn't caused any issues for me in the past 4 years as a daily driver. For anyone Googling for answers I'd say some of us have had success and some haven't. It's inconclusive. But for the OP who's invested in this already, a manual GTT ECU can work and might be worth a try compared to the GTT auto ECU which will be a pain for the reasons already pointed out.

You could just try and sell the auto ECU, keep the Nistune and put it in a GTT manual ECU. That will allow the existing NA TCU and wiring to run the gearbox. That's what I've got on my NA+t and is 'almost' plug and play. It won't be a GTT but it'll get you to the next step of sorting out the map.

This article appears to be talking about the swirl valves ... https://carscanners.net/nissan-skyline-r34-and-laurel-c35-with-rb20-de-neo/ And this is one of the old discussions with dead pic links. https://www.skylineowners.com/threads/rb20de-r34-gtt-neo-engine.155290/

Back to your original question, the RB20DE NEO has butterfly valves for swirl (see page EC-3 in the R34 manual). I remember seeing some pics once but so many pics have dead links now I can only find the discussions by googling. So I can't remember exactly where the valves are - in the runners maybe? The RB25DE NEO doesn't have them although both have the variable air intake butterfly valve in the inlet plenum.

I'm running a stock NEO non-turbo AFM without any problems. I'm using GTT injectors and stock GTT ECU. At first I kept the NGK BKR5EIX iridium plugs that I already had before the turbo conversion. Not ideal maybe but they worked ok. I've been running the conversion for 3 or 4 years. Recently I did have a misfire that felt a bit like hitting the rev limiter. I found some Splitfire coil packs on a spare engine I have so fitted those. At the same time I changed to NGK BKR7ESC-11 that one of the tuners here in the UK recommended for my +t and that misfire is gone.

I'm sure someone will come up with a better suggestion more local to you but here in the UK, Conceptua are a reputable dealer who stock these for the non-turbo intake and will post worldwide ... https://www.ebay.co.uk/itm/New-Throttle-Body-to-Plenum-Specs-Gasket-For-R34-GT-Skyline-RB25DE-Neo/111878477184?hash=item1a0c7a1580:g:5D4AAOSwoydWnOLe Alternatively use https://nissan.epc-data.com/skyline to find your model and in the engine and fuel system section find the manifold gasket and click through to the amayama shop and have it delivered from Japan. I've had stuff sent to the UK this way no problem. Import tax and waiting a couple of weeks is a pain though. But I thought you guys over there can buy most stuff off the shelf?

Fuel filter made no difference. I might just let it go now and not worry about it as the issue is negligible. Or if I can be bothered I might check the pump is still mounted in the tank ok and might swap the AAC for my spare cos years ago I lost the spring while cleaning it and replaced it with one from a ball point pen ? Anyway re. the direct voltage conversion, I checked the wiring diagram and thought I'd post this in case anyone else is interested. I believe that stock GT wiring will run the fuel pump at 13.5V as standard. In the attached wiring diagram, red lines I've marked are all battery voltage from the ignition switch and I've taken a confirmed reading of 13.5V at the solenoid plug I've marked. The fuel pump dropping resistor (and control module) don't exist on the non-turbo so the other side of the pump is direct to ground (green line on diagram). So although I haven't measured it directly at the pump, I reckon that means a non-turbo car will already have full battery voltage at the pump. Happy to be corrected if I'm wrong though.

Interesting point about the pump. Here's a pic from another thread showing what I had to do to mount it in the cradle. I think a Walbro 342 would have fitted better than a 341 but I tried to make sure it was secure. But in theory the hose clip could have slipped and who knows! Maybe I'll check that. Ordered a fuel filter too as it's about time I changed that.