discopotato03

GTSBoy I never got the full story on what the exact head differences are between R33 and Neo turbo heads . I know the Turbo Neo chambers have a smaller capacity than the R33 RB25 ones but was never sure if they were shallower or the valve angles different . Also not sure how much smaller their inlet ports are . I think I read that the Neo Ts torque peak is significantly lower than the 33 DETs but as you said different cam profiles are a significant part of a system rather than a major change in isolation . If I was ever to rebuild a 33 spec 25DET it would use Neo spec pistons rods and head . Neos were the last RB25T revision roughly five years after R33 25DETs , factory engineering is difficult to beat particularly when the trend was towards more power/lower torque peak and lower emissions - read lean mixtures with efficient combustion (reasonable timing numbers) . A production road car is mainly about was sort of torque and drivability you get at part throttle loads . Efficiencies here are generally what emissions and consumption is all about because that's where a road car spends most of its time . It all changes at wide open throttle and full power at revs can be compromised to a degree . Very likely why the GTt had a slightly larger SMIC and turbine housing . I personally don't think porting (modifying) is that important on an RB25 head unless you expect really high numbers and then a 26 is probably a better (less compromised) basis to play with . They don't pretend to make great part throttle lowish rev torque and the ITBs etc are aimed at better cylinder filling in the upper half of the rev range . AFAIK the ports/chambers in a 26 head aren't majorly different to R33 RB25 ones , Nissan just changed the side water jacketing and manifold bolt patterns to stop you cross dressing manifolds between 26s and 25s . On paper the Neos 206kw isn't far short of the 26s 209 and a Neo with 26 manifolds and turbos may have made the by 1998 ageing RB26 look a bit pedestrian overall . Hate to say it but all RBs are dinosaurs by todays standards . A .

I think people sometimes try to get really involved in head port work when in fact the manufacturer had most of the smarts happening for the era of the engine - particularly a performance enhanced one . True they have emissions and some sane sort of consumption targets to meet but these RB heads are not dogs . The limitations Nissan put on them were based around pretty tame performance numbers and fits in with quiet clean and acceptable consumption . Once you improve the external inlet and exhaust tracts you can make pretty impressive power without major feats of internal reengineering . Generally with production cylinder heads the greatest restriction to air flow is the inlet valves themselves , controlled by the standard valve train . If the ports were a major restriction higher performance cams wouldn't achieve much . Also something to think about is that valves obviously aren't always open so flow will change with how far open they are in the lifting/closing phases . In think in a road driven car the easiest way to improve internal air flow is a set of drop in aftermarket cams because they take the least effort to do , especially if its belt and tensioner/idler time . Once you start modifying a head casting there is no going back if its botched . All I'd ever do to a street mild track RB head is to clean up any casting flash and smooth any machining marks in the throats . Have a look at the dyno threads , plenty of examples of high outputs with little or no head porting . As mention forced induction is a huge advantage in getting more air through inlet ports . I would be very wary of big ports in an RB head because port velocity is important when it comes to mixing and carrying atomised fuel into the cylinders . Making impressive power with turbocharging generally isn't difficult , keeping all the drive it round the street part throttle torque and flexibility is where the wheels fall off in too many cases . Better to have the best of both with the fewest compromises . Your call , cheers A .

The idea is to have a bolt in 3.9 ratio diff with the right side flanges to suit my drive shafts , and tailshaft . From KAAZ part numbers you can see which S14s and R33s use the same carrier or hemisphere if you like . As for carrier offset , some on Silvia boards describe this as the "thickness" difference between crown wheels of different ratios . The change over seems to be between 3.9 and 3.7 and someone reckoned the RWD Skyline 4.11 and S14 3.9 are the same - handy . Also all short nose R200s apparently use 12mm crown wheel bolts . So with an exchange of carriers and back plate it could be an easy way to get a slightly taller final drive using all factory parts . I researched GTR R200s a few years back and from memory they used larger diameter R230 side stubs and it sounds like S15 manual turbo and R34GTt are similar/same . A .

From searching around I think the go may be to buy an aftermarket LSD carrier ie Nismo or Kaaz that comes with the correct 5 bolt side stub/flanges . These are supposed to work better than the OE Viscous center not that its a big issue ATM . So the next question is will an LSD carrier for a GTS25T fit and work in an S14 or 15 non ABS diff assembly with taller ratios ie 3.9 and or 3.7 . I remember reading that R34GTt and S15s had larger stub diameters like GTRs have . Basically will say an S14 (SR20DET) 3.9 non ABS diff take a Skyline carrier and bolt in with the Skylines rear cover plate ? Are the input flanges same R33 RWD/S14/S15 ? Thanks , A .

From pics I've seen the ABS sensor is in the nose of the casing which is a tad longer on ABS equipt R33s (RWD) . I think RWD R34s have the ABS sensors on the sides for 4 channel or four sensor systems . And the shorter short nose case like non ABS RWD R33s . R33s must have had 3 channel if fitted . I suppose the way out with the side stubs if Silvias didn't have 5 bolt is to fit a Skyline carrier in the Silvia diff case keeping its original crown wheel . I've been inside older long nose R200s and H190s swapping hemispheres and the only dramas were offsets between different crown wheels . Oh and also crown wheel bolt sizes . Does anyone happen to know if the carrier offset is the same with Skyline 4.11 and Silvias 3.9 and 3.7 ?

Before I start I did search here and other Nissan boards ie Z32 and Silvia / 200SX ones . From what I read an S2 R33 GTS25T manual uses a short nose R200 VLSD in 4.11 ratio and with 5 bolt side stub flanges . Non ABS R33s have the shortest nose because the ABS sensor versions are slightly longer . I did read here that S2 R34GTt and S15 200SX use the same short nose length and it sounds like they use the same 5 bolt side flanges as my R33 . Does this mean that the S15 diff bolts in maybe with a change of rear cover and would give the 3.69 ratio and the helical/Torsen style LSD ? If not is there a bolt in 3.9 ratio option for non ABS R33 . I'm not after opinions on why the ratio change just the interchangeability facts . Thanks in advance cheers A .

Almost certainly more expensive and a bit heavier , sounds like more lead in its plates . I think from memory the Century Ultra High Performance version is called a 68 but check before buying . Physically same dimensions as the High Performance 58EB I have . An 820CCA battery would no doubt start an RD28 Diesel six . What battery is your one ? A .

My prediction - if everything else is good is maybe 230 270 and 300ish (assumes 0.68 GT Pro T housing) at the wheels on E70 . Any BB Hitachi is limited by small fragile ceramic turbine . Most people reckon the GTRS is ok but restrictive on the hot side for an RB25 . 2835 Pro S basically GTRS with a bigger trim compressor and next size up (and cropped) turbine in larger HKS housing . People say you lose that boost/torque right down low that Hitachi and GT28 based Garretts have on an RB25 but they feel pretty good for a mid range all rounder . OT but I want to see Garrett try that 76mm 9 bladed billet compressor from the GTW3476R in a GT30 BB turbo . GTW3076R ? A .

Actually people I stuffed up with which Century range battery I bought . If I'd looked at the Ultra Hi Performance instead of the High Performance range I could have had a 620 rather than 540 Cold Cranking Amp rating in the same physical size . Bugger ... A .

GTRs use a three step earth return system for the fuel pump . The fuel pump control module has switching to allow high resistance (two resistor banks in circuit) , low resistance (one resistor bank in circuit) or no resistance (no resistor banks in circuit) . There are from memory two wires from the ECU to the FPCM to switch in/out bypasses for the two separate resistor banks . If you've tried good FPCMs and you still don't get an earth return for the pump the issue may be upstream of it so no matter what it does you get an open circuit . If you can get the relevant wiring diagrams you could try running your new pump earth to the appropriate FPCM wire and create a new earth on the down stream side of it . You know your new earth circuit works so if you splice a healthy FPCM into it the system should work like Nissan had it . A .

Quest was an American spec Nissan van/people mover With a V6 VG33 under the lid . We only got that engine in from memory D50 petrol Pathfinders but not the Quest higher output alternator . Also alternator brackets even on VG's differ depending on what car they came in and whether it was oriented upside down or not - meaning adjuster bracket facing up or down . Late V6 accessories/drives can be a nightmare . Even so the Quest alternator needs mods and there are write ups on American boards like fresh alloy.com . The thing people who haven't played with these higher output Japanese alternators often don't realise is that they are larger in diameter than your typical Nissan RB/SR/KA 90s era ones and they can be a pain to wrestle into place like around an RBs lower radiator hose . They are also appreciably heavier than an OE one . Some mite say so what but if you have to drain/refill/bleed cooling systems it isn't a simple R&R anymore . Also Nissan made life hard by casting the RBs lower alternator mount into the block rather than using a bolted on bracket like the older L series block has . what comes off can easily be replaced with something to suit a non std alternator in an ideal location . To be honest I solved all my problems by having the std RB25 (33) alternator rebuilt with new regulator and diode pack , and using a larger capacity battery . Admittedly I don't have high demand pumps or sound systems and if I could track down a reasonably priced GTR alternator I'd freshen it up and use that . BTW when your auto sparky can't find a reference to an R33 GTS25T alternators part number tell them to cross reference EB Falcon six parts because their std alt is internally similar/same . . I think GTR alternators had an extra 10a output capacity , 90a , and I'm not sure what was internally different probably minor rotor upgrade . A . A .

Yes 2 years . Engine sounds like its lifting out of the mounts on cold starts now . A .

Hi all , recently killed another battery which was a Century NS60S 430CCA claimed standard replacement . Never liked these because I thought they were too small and more like a 4 cylinder battery . I went to Batteries Direct at Peakhurst in Sydney because a friend works nearby and recommends them . I wanted a battery more like 530 CCA and one that can fit is a Century EB58 which is intended for Fords . Length wise basically same as NS60S but wider and fits between the alternative mounting rod holes . Also these are a large pole battery unlike the small ones in the previous battery , never liked those particularly the smaller earth one . My earth lead had been remade to a larger one with the std two hole fitting reused and an eye fitted to the battery end . I bought new terminals with rings machined in their holes to bite in a bit better . They connect to the cables with a stainless eye bolt . I had a spare positive cable from a wreck so I cut the outer part of the pressed clamp off and used the original hole , enlarged , to bolt to the new terminal . Also bought a new clamp bar because the old one isn't long enough . So now have a wider 540CCA battery which should crank a cold RB25 over a bit better this winter . Take care cheers A .

A tuner has told me that 740s tune up better than 555s , those aren't supposedly real good at idle . If staying on petrol also consider the S15 injectors as they a bit bigger than R33 370s . A .

Out of curiosity which Blitz return flow are you using as there were two sizes of the long lower pipe . Mine I believe is the earlier version with the larger diameter lower one . It may not make much difference but occasionally things like this can . A .

Do the R34 Neo specific issues disappear if aftermarket or R33 inlet manifolds are used ? I keep wondering if the I think smaller Neo inlet plenum section is working against performance and needing higher boost pressures (and compressor outlet temps) to push beyond 300+ . It would be interesting to hear from someone that say put a Neo 25T engine in an R33 with the 33 inlet manifold system . Long shot but 33 inlets could be a cheap upgrade on Neo's pushing beyond 300RWKW .

I thought the 0.87AR GT Pro S turbine housing was the harder one to find .

The smallest one in this series is the only one I had any interest in , from memory a 76ish mm 58T 9 bladed compressor . As was mentioned the turbine side doesn't sound very exciting . That compressor on a GT30BB cartridge may have potential - if Garrett ever decided to offer that combination . Garretts issue is it never seems to offer anything new turbine wise , mostly the old T series grow balls and even machined compressor wheels . It started with the T4Rs and T04Rs (T04Z) and now the latest GTW series .

Current brew is a 50/50 mix of E85 Lime and 98ULP . My engine was getting rough on E70 and I was beginning to wonder about the gum gunge some people get on their injector tips when using high eth fuels . I did use that ethanol fuel conditioner for a time but ultimately it didn't change the rough running much . I started blending more ULP into the Eflex to get acceptable consumption and picked up 30L of green E85 for a 50/50 mix - as easy as splash blending gets . Results look pretty good so far with power and general consumption . I suppose the octane would be around 102-103 which isn't far short of the old E85 but 57% of the fuel is now PULP which gives better consumption than 85% ethyl alcohol . The down side is that Uniteds Green gut rot is a bit exy . A .

I'm hoping this doesn't turn into dump pipe wars , I just think that for the effort and expense involved making divided ones isn't worth it . The flange plate absolutely has to match the housings inside profile meaning that if the dump side doesn't , function wasn't its primary objective - cost cutting was . Its obviously more time consuming to profile cut the inside of the plate than it is to run a hole saw through it . I reckon 3.5" tube welded to a properly made GT30IW flange plate with a decent gusset isn't going to lack flow potential on a typical RB25 install . Plenty of exhausts are 3" and they can support good power if the whole system is made with good mufflers cats etc . A .

Some have had Garrett compressor housings , usually the give away in any RB25 OE comp housing is the anti reversion groove machined into the inlet snout that generally lines up with the tips of the inducer or inlet comp wheel blades . A . PS the VG30 single ceramic BB turbos don't have this groove and the comp wheel was slightly smaller . Plus the actuator and its mounting bracket is different to any RB based OE turbo .

I looked very hard at their GT30 integral dump and opted to have an open mouthed dump/front pipe made . If you look at the inlet of the waste gates bypass its round where the turbine housing isn't , maybe convenient to make with a hole saw but questionable functionality . Hard to believe there wouldn't be a pressure rise here and anything that does this downstream of any waste gate can effect its performance . I bought an XR6T turbo side GT30 IW flange plate from Carlton Mufflers because theirs is thick and thick is good when you have to weld to it . Kirawee Mufflers made the front pipe in I think 3.5 inch tube and formed a gusset for the gate outlet section . I never have creep issues and with the same housing as yours . 1 bar large can actuator and the brain box does boost control . IMO except for big budget race apps where everything is flow tested split dumps are more trouble than they are worth . If you really want to separate the two exhaust streams and the turbine housing casting doesn't have a short divider build one into the flange plate . If you are really concerned about pressure build up behind the T housing then use larger bore tube here and neck it down at or behind the cat . My system is 3.5 inc the cat and its conical outlet was made the reducer to 3" . My exhaust is higher flowing and noticeably quieter than the Japanese name brand POS it replaced . A .

I don't think I've ever seen great consumption out of any R series Skyline . I think its a combination of short JDM gearing and the era these engines existed in . By todays standards they can't run lean mixtures and still perform acceptably . Correct me if I'm wrong but didn't ADM S14s and 15s get taller gearing than the JDM ones , something like 3.7 vs 4.1 diff ratios ? I always thought my GTS25T could have used a 3.9 or even 3.7 final drive just to have a bit more speed , or less revs , in the gears . I reckon slightly lower cruise revs and a slightly more open throttle would work better with decent tuning . Just my 2c cheers A .

Interesting story . My take . I don't think any RB25 was designed at Nissan to be a real power house in that engine family . They certainly didn't use it to go racing with . A lot of things could be affecting your power and boosting characteristics and one I reckon could be the 25s inlet manifold design . What Nissan wanted was reasonable power output but more importantly good part throttle torque because that's what 90% of a road engines life is spent at . Its basically a hole on one side and six on the other so when you try to feed really high airflows through it isn't ideal . Nissan wouldn't have gone to the trouble they did with the 26s manifold if the far simpler 25s effort worked well enough . Turbos . I think the GTX3076R is a bitzer because it has closer to GT3582Rs pumping capacity without the bigger turbos compressor housing or GT35 turbine . My gut feeling is it may work better on smaller higher revving engines like Hondas etc . Often race engine turbos have quite big turbine sizes in relation to their compressors but they can also work over narrower rev ranges . You could also look at that as a small compressor for the turbine size because it means the same thing . Personally I think for what you're trying to achieve an RB26 would have been a better basis mainly because of its head and inlet manifold system . Anyone who fabs exhaust manifolds can make them suit both stud patterns and some do . I once went in a VL that had an RB26 and a GT3582R/1.06 AR - ext gate . It came on boost in the 3500-4000 range and actually needed a larger gate to make good power up high . Gas flow on that engine should have been pretty good both sides and I think it had a 4" exhaust off the turbine housing too . A .

My take on "squish" and detonation is different . I believe short flame paths mean most/all of the charge is burnt quickly before it gets the chance to heat and auto ignite . If the gap between the piston and the "quench pads" could be zero then the volume and last gasses to be burnt would be zip too . Naturally you can't do this because pistons and rods effectively stretch (higher revs more inertia) and eventually the pistons hit the head . Something else to remember is that no RB head was designed specifically to be a competition solution so factors such as packaging compromise the design and effective performance . A purpose built comp twin cam head often has narrow included valve angles so the chambers can be quite shallow and ditto piston crown valve reliefs . I believe Cosworth BDA heads are like this are they are hardly current cutting designs . From a production engine perspective narrow valve angles (inlet to exhaust) make the head casting tall and that doesn't fit well in sporty cars with low noses . One thing that wider valve angles does suit is heads with ports relatively low down on the sides , reduces the flow angle on the backs of the inlet valves . The reason low ports are good for crowded low engine bays is that the inlet manifold can be more compact and lower in height . Personally I would want a very good demonstrable reason to remove the quench pads from an RB26 head particularly one on a higher capacity block . My reason being the greater the engines capacity becomes the less the issue with chamber volume becomes . It gives you freedoms with piston crown designs because you don't need substantial raised sections on the piston crown to get the static CR up to a reasonable figure . Great lumps of aluminium have often been put on pistons because the CR took priority over extreme power potential . In an ideal world I'd like RB25 Neo sized chambers on a 26 head and more ideal piston crown design than R33 RB25s and all 26s have . Sad fact of life is that the RB26 design is an escapee of the late 1980s and its showing its age . My 2c spent cheers A .