discopotato03

That open tube you have needs to be plumbed in upstream of the throttle body . Its the air supply for the Idle Air Control Valve . In standard form it connects to a barb on the original crossover pipe - upstream of the throttle body . A .

Yep I see what you mean R33 TB wise . The Neo plenums mount flange doesn't have the extra material to cover the back of the barbs hole like the R33s plenum does . Thanks but I know someone who I think still has R33 upper and lower manifold halves bare . What I want to do is measure the diameter of the ports where the upper and lower halves of the R33 version bolts together . I measured the Neo Turbo version and the ports are just over 41mm diameter - around 41.2mm . The Neos shim gasket is a very neat fit here . A .

Ah , I was going to ask the differences but thought I'd better search first . I'll have a look at my R33 soon to see what that vacuum hose goes to , I suspect the charcoal canister . Yes I knew about the top of the manifold ports being different , the head ports are supposed to be the same in this area R33/R34 . Cheers A .

I managed to get my hands on an almost bare and a complete Neo turbo inlet manifold to play with because I think its a better setup . I don't have an R33 to compare atm but I know someone that does . I want to measure the difference at the ports and where the plenum mounts on the lower section . As we know the TBs and bolts interchange , one thing is the 33s TB gasket is steel where the 34s is paper . The 33 has a rubber gasket between the upper and lower section where the R34s is steel shim . Something I need to find out is the ID of the coolant hose rising up from that fitting on the block behind the water pump , it connects to the Neos front bleeder section . At a glance I think the R33 is ~ 8mm where the Neo could be 10mm . Its that hose which heads down next to the front rubber fuel hoses . A .

Hi Noobles , can you get back to me about the manifold please . Cheers , Adrian .

Your call but I'd be looking for a Garrett GT30 IW turbine housing in 0.82 AR size . That's unless you want to run an external gate on it . Shame to weld up an original HKS Pro S turbine housing .

HKS did GT Pro S turbine housings in 0.68 and 0.87 AR sizes . I'm not sure if the 0.68 AR one would get 350 RWKW especially on PULP . In theory you should be able to use a Garrett T3 flanged IW turbine housing on that unit and most opt for the 0.82 AR size on RB25 turbo engines . Those Pro S turbine housings were gold in the days before Garrett were making integral waste gate housings of their own - which are same format as the Ford XR6T T3 IW turbine housings . A .

That will almost certainly be a HKS GT3037 Pro S , assuming it hasn't been interfered with . They look virtually the same as a GT"2835" Pro S except the turbine and compressor are larger in diameter . GT3037 is HKS speak for what Garrett calls a GT3076R in 56 compressor trim . Pro S is for their unique compressor and turbine housings . The turbine exducer or outlet diameter should be around 55mm . Cheers A .

Not identical but the R34 one works fine in my S2 R33 . A .

Interesting stuff . With coils are they electrically the same R33 to R34 . Would a set of either work if you had a suitable coil loom . From what you're saying the physical difference is the orientation of the connectors on the coils themselves . As I said previously I think I bought a new Neo coil loom and it plugged straight in . I don't think the tabs under the coil cover were exactly the same but at the time I wanted new wiring for the new Splitfire coils I fitted . Cheers A .

Well with the GTt setup you'd have to find a way to close that cold start side or use an adapter plate and possibly an R33 or SR20DET type IAC assembly . If aftermarket your ECU may allow you to adapt an alternative IAC valve assembly that's big enough to do cold start and idle speed control electrically . Aftermarket manifolds are never easy and many people reckon that in a road driven car performance can be less except right up high . Something to weigh up .

I mucked around lots recently with R33 RB25/N14 Pulsar GA16DE/S15 SR20DET IAC valves . Make note that the Pulsar N14's GA16DE version uses a smaller internal shuttle valve size , R33 RB25 and S14/15 SR20DET are same . That aside , generally people use an adapter plate to fit R34 GTt IAC valve assemblies on the cast GR/Fredy manifolds intended for R33 RB25 . With a bit of a rejig you could probably mount an R33 or S14 or S15 IAC assembly because none of these use the water heated cold start valve (AAC) .You can change the air pipe tube over between these last three IAC units to get R33's T shaped junction tube . There is a mounting pad on R33 and R34 RB25DET water pipe that bolts underneath any of these inlet manifolds . This is where the R33's AAC or cold start bypass valve mounts . I tend to agree that these aftermarket manifolds often create as many problems as they solve and most reckon the R34GTt's OE inlet manifold is pretty adequate anyway . The sad fact of life is that no aftermarket RB25 inlet manifold lets you put the cold start/idle stuff where it needs to be . I once thought removing the factory crossover pipe was a major PITA but once its been off a few times no biggie .

I imagine the cold start portion of the IAC assembly , wax pellet part , will stay open and the idle will stay high . You need to run coolant through them for it to work as intended . Originally it gets coolant from three places . The standard manifolds cast in water log , the fitting into the lower drivers side rear of the head , the rear of the original manifolds throttle body . The GTt's IAC housing is meant to be a high point in the original cooling system which is why it has the air bleeder bolt . A .

Update , bought a couple of late S15 IAC valves cheaply and fitted the cleaner one with the R33s T piece . Also had to turn the IAC solenoid around so its socket faces upwards like R33 . Downside to late S15 IAC assembly is a return to a plastic idle speed screw which doesn't interchange with the earlier brass ones . It does work a bit better but I'm beginning to think part of the issue is computer settings ie letting the valve park itself slightly open at low revs . Some computers want to hold the valve shut until the engines virtually at idle speed resulting in an undershoot at return to idle . Just on idle speed screws . Many of these get hacked up and I thinks its because people use Phillips head screwdrivers on them . Phillips is a bastard of a system because it was a production system designed to cam the driver out if overloaded , this also butchers the screw head . Before the Phillips system came out the Japanese developed a cross head type driver and called it JIS for Japanese Industry Standard . At a glance JIC screwdrivers look like Phillips but the taper on the point is less and they don't bottom out as easily . Bottom line is they fit and grip better and do less damage to the screw heads . Real Japanese JIC screws have a dot next to the cross and Phillips screwdrivers kill them . JIC screwdrivers fit both screw heads and in my experience work better on Phillips screws . Vessel make JIC screwdriver sets and they work well . A .

I agree Neo 25T far better engine and using as much of it as possible is way to go . My understanding is that the only significant bottom end difference R33 to R34 RB25DET is the pistons and rods . Pistons crowns are lower to keep the same 9:1 static compression ratio and the gudgeon pin size is the larger 26 spec to suit 26 rods . If you decide to rebuild then Neo rods and pistons = Neo bottom end . Recently I've been looking at 33 and Neo inlet manifolds mainly concerning plumbing differences . Idle air control and "auxiliary air control" (cold start bypass valve) are completely different with the Neo , simpler because it has hot water plumbed into it rather than the clumsy R33 air valve plumbed underneath . Also the IAC assembly has an air bleeder on it and the manifolds cast in water log has a riser pipe up to it . I'd loose the Neo throttle body and keep the 33s one and its TPS . Neo's appear to have another air bleeder in front of the cast water log with another riser hose up from the thermostat areas pressed in block fitting . Long short Neo inlet manifold has better IAC system and takes better top feed injectors . Manifold runners are supposed to be slightly smaller bore and it looks like the plenum volume may be slightly less than R33 . With the same external mods Neo's always seem to make a bit more power than 33 spec 25DETs . I could be wrong but I'm pretty sure I ordered a Neo coil harness new from Nissan or Kudos and it plugged strait into my R33 . A .

Neo RB25 minus cams injectors and hot side manifold turbo etc .

I think people should look at all the valve timing evens which means more than just cam lift and valve seat to seat duration . Quite a few aftermarket cams are compromised so that they drop in with few or no modifications . Obviously priority no 1 is not killing the standard valve train . I'll see if I can link the Tomei USA page where you can look at all the numbers ie lobe center lines and overlap timing for their cams . https://www.tomeiusa.com/cam_spec/cam_spec_list-e.html I've never looked at aftermarket SR20 cams but if they are anything like RB25 Poncams they'll have a lot more overlap than the factory standard cams . Cheers A .

Found out a bit more today . Found another 2 Pulsar N14 IACs and when the epoxy was removed one had a cream coloured plastic bung and the other the brass one . Also got to play with a 97 U12 KA24 one and it was plastic too . I suspect the R33 ones are plastic and if you attack them through the epoxy they break up , the give away is the base with the hollow boss that locates the spring and the end of the hollow shuttle valve . Also the springs are different rates in these IACs , found soft medium and firm ones so far . A .

To add a bit more . I discovered the de-epoxied brass bung makes for a slight vacuum leak to the inlet plenum . I'd say the epoxy on the IAC units with the bung isn't just there to allow factory pre-setting (on the early ones) and prevent tampering . If it was designed to be adjustable it would have a seal something like the idle adjustment screw has . I got a small bottle of Loctite aircraft gasket sealant which never sets hard , I think a smear of this on the threads should minimize the leak and stop the bung moving with vibration . A .

Thanks , that sort of confirms that Nissan cheaped out with the R33 RB25 IAC assembly so don't attempt to pull one apart if you don't have that brass plug . I'm not sure how but I think my engine must have an air leak into the crank case or cam covers because it wants to pull so much air through the PCV valve at idle . It does have the hose from the exhaust side cam cover to the turbos air inlet with a brass reducer with an approx. 5mm hole in it . My engine doesn't like how much air it can drag through when as the factory had it though Nissan used MAF sensing rather than MAP . A .

Got stuck in last Saturday but something to approach with caution . Removed the R33 RB25 IAC assembly and gutted it of all internals . The biggest surprise was that the epoxy gunge in my unit went right through to the outer spring base - in other words no brass plug . Luckily I had the Pulsar one because Nissan had the female thread for it to screw into . Had to buy a thread file to clean everything up enough to work . Its all back in now with a dab of silicon on the outside of the plug to stop it turning . The internals are slightly different on the Pulsars shuttle valve ie smaller diameter valve and guide . With the steel tube junction just place that in a vice with soft jaws and turn the casting to sort of twist it out . Went back in fairly easily . Sadly none of this fixed my idle problem but it could work for others . I noticed my engine making a distinct sucking noise through the PCV valve and pinched it shut , idle speed drops . ATM I have an old brake hose clamp keeping it shut and adjust idle speed to suit . It is now better , but not perfect , though the ViPec software shows lower manifold pressure at idle and over run and throttle response is much better at low revs . A . Nearly forgot , the tool you need to fit the narrow concave slot in the brass plug is called a "Dzus" tool or screwdriver . These look like a very wide thin plain blade screwdriver but the blade is slightly convex rather than straight . They are intended for some aircraft and motorsports fasteners .

Ok . I retrieved the N14 IAC housing I beat up trying to get the brass bung out . Its now gutted and cleaned up at home . I can sort of see why these assemblies are expensive but the Australia Tax makes them stupid expensive . Anyway there was a fair amount of machining and threads in the alloy casting and they have a stepped brass bush pressed into them . I think the problems are mainly the spring relaxing and not allowing the tapered section of the sliding pin valve to move back into its bore hole . It doesn't actually seat against the shoulder unless the solenoid gadget is removed . The parallel section is a neat enough fit in the brass bore not to pass air until the tapered section is exposed , if the spring tension is weak the sliding pin obviously isn't pre loaded enough . It's supposed to have spring loading from both sides ie the spring on the brass bung side and another in the electric solenoid side . Obviously if the one on the bung side is weak then the one in the solenoid side wins and the sliding pin is biased away meaning closer or at the point of exposing the start of the taper . I just wish Nissan hade made a way to have the bung adjustable ie longer and fixed with a lock nut . Long short I think the best fix is to remove the epoxy/bung/spring/sliding pin valve and clean everything properly . Then refit and adjust the spring tension till it works properly . Then remove and use a tiny dab of thread lock to stop the bung screwing itself in or out .

I just found these . http://www.skylineowners.com/forum/21-tuning-technical-questions/135514-aac-valve.html And this . http://www.southernskylines.com/howto/r33/aacv_aac.html Obviously its a common problem but not too many people talk about it . Lots of agro for and time weakened spring . A .

Thanks for that but again , how did you get the T piece out without damaging it . I'm off to a U Pull it wrecker now to try and get one off a 93 Pulsar GA16DE , they are same thing but with a straight tube out of the IAC body .

Sorry wrong issue .