Dale FZ1

Agreed

Neither Al nor Cubes seem to have any boost control issues. What does Slide mean? Boost running away, or falling off as rpm rises? The sort of bottom end power density offered by the 0.82 means you can probably afford to be quite lazy in driving the thing - torque on demand and pull higher gears easily. That may require a bit of good throttle control in slippery conditions. By comparison the 1.06 would be a tad more progressive in delivery and maybe stretch the nose-over point closer to 7000. With the amount of torque produced by a 30DET able to be put to the ground a touch easier but require more downshifts when you want it to really jump. Depends if you see value in having it run like that or not but definitely not a bad choice.

What rods, rod bolts, harmonic balancer are you running? How hard do you intend to rev the thing, and where is the target rpm range for best torque production? Have you had any advice on the cam specs and what characteristics they will give the engine? For me, all those factors will play a role in whether the 1.06 is really worth using, but I like your thoughts. Both Al and Cubes have had good results with the 0.82.

The difference in this case Cubes is that it's apples for apples. Both housings are GT30 IW originals rather than the different styles Lithium used. Adrian I think there are plenty of off-the-shelf solutions that work well without going to that level of custom building. I know of someone else who is getting ready to install a complete 48T GT2871 0.86 A/R and use a T25-T3 adaptor. I wouldn't expect it to make the same numbers as a 3071 but will be interesting to see the results given the amount of discussion this 3071 has had over time.

It depends if the system is spec'd properly and set up well enough to allow the cooling medium to shed its heat. Pump the coolant around too fast and it won't transfer its absorbed heat via the coolant radiator. Likewise if the coolant radiator is too small or is inefficient there will be problems. The only identifiable disadvantages I can see are weight, cost, complexity when compared to air:air. You'd need to look at those factors plus engine bay packaging before going away from a conventional front or side mount air:air for a Skyline.

Everyone has different ideas, and that’s what is good about engineering. There are always a number of solutions to hit on a particular outcome. I’m not suggesting that the intended purpose of the wastegate is to regulate anything other than turbine speed and therefore limit the peak mass-flow through the compressor. – but the venting of gases most certainly reduces TIP as a side result. That the 0.63 IW GT30 housing can’t vent sufficiently at least on a RB25 is proved by Dave’s boost running away. For that reason I’d suggest he is on the right track to control that spec setup by using a bigger more efficient vent orifice available via an external gate. Choice of A/R effectively shifts the torque curve to the left (for smaller A/R) or to the right (for larger A/R). There’s no secret about that, and if talking about diesels have a look at the current high efficiency common rail offerings. The small capacity 2.5 litre Navara runs variable turbine geometry to effectively get it into boost at low engine rpm and yet breathe effectively at high rpm – so it’s still about area under the curve in that application. Bump up torque at both ends of the scale and you have a strong performing result. The variable geometry allows proper control of turbocharger speed, but also has an impact on TIP and mass-flow capability of the turbine. Unfortunately that technology is not readily available or economically applied to our Skylines so no point wishing. The point is that in each instance yes, there is a mechanism in place to improve overall engine performance compared to a free-floating turbine – and that mechanism simultaneously should control turbine speed + limit the TIP. Where skyrocketing TIP becomes a real concerning issue in my view, is from the point of targeted peak engine torque production through to maximum engine speed. Why? Because that’s where pressure differential across the engine is most affected and scavenging + heat buildup can become a problem for tuning and engine reliability. For all those reasons I think the 0.8x IW GT30 housing is the better choice for the 3071 cartridge for simplicity of packaging and economic constraints. Dave’s idea of the 0.63 free floating spec + external should really do the business but it comes at a cost – and over time we have seen threads discussing appropriate placement, angle of incidence etc of external gates. Get that part wrong and there is still potential for headaches. Finally despite all that, I don’t know whether the 3071 0.8x IW combination is going to offer any significant benefit or different driving feel to a 3076 0.8x IW. I’d have been happy to swap cars with Gary to find out, but believe me when I say the 3076 on an RB25 is not laggy or lacking in progressive delivery. However it won’t have the punch at 2500rpm that Dave commented on. I know of someone who is shortly going from a 0.63 IW to 0.82 IW setup to trial on their RB25 so there will be the chance of hearing first hand back to back experience. cheers

I'm pretty much on the same page as you Dave - after studying the 71mm compressor map at length I decided for it to perform it would need the higher/earlier rotor speed (vs the 76mm) to make the engine make torque down low. Chasing area under the curve and delivery is where it's at for me. Far better to forgo 10kW at the top end if you can make +45kW in the mid range. And there is no doubt that the engine will only make big grunt in a supercharged (force fed) state, so if the turbine A/R is too big to keep it away from that transition state, it will definitely only be (at best) as good as a similar spec N/A engine. Perhaps worse, as Disco indicated. In short, it needs the charge density to make the bigger bangs and torque. My thoughts/comments were directed towards housings fitted with internal gates, and any "dramas" I perceive are of the boost control variety. Unfortunately the physical dimensions of the housing/gate just don't seem to provide adequate venting to control turbine speed. Get the 0.63 in non gated and match up with a decent 50mm external gate setup and it is likely to be very different. Something else maybe worth commenting on is the notion that wastegates aren't designed to reduce turbine inlet pressure. I'd have to disagree strongly on that one - a gate is designed to control turbine speed by venting mass flow. If the mass flow is being crammed through at such a rate that boost is skyrocketing, then so is TIP. Logic tells me that by venting the extra mass, then pressure within that housing scroll has also been reduced by a proporionate amount. By using a wastegate of suitable flow capacity it should be feasible to use the 0.63 housing and essentially move the torque curve to the left as Dave wanted. The only trade off in that setup is component cost and whether the fall in high rpm efficiency is a problem in that application. cheers

Check with BHDave, or search his threads. He had boost control issues with a GT30 0.63 combination. I suspect you'd be dealing with similar issues. With that spec turbo you'd have to be chasing some pretty big power output, and an 8psi actuator seems seriously underdone. Go to a 0.82 A/R housing and fit a 14psi actuator at minimum - choose an actuator that is close to your intended boost and fine tune it with your controller from there. If chasing high output from your RB25 then I hope your plans and budget extends to engine hardware upgrades - it will only stand being leaned on for just so long before something gives out. Keep on it, and keep us posted. Very keen to hear how this combination works especially if you have a manual transmission. Hopefully your turbo supplier is willing to work with you on this one.

Over time it has become clear that a few factors will impact on “correct” choice for turbine A/R. I’m the fortunate custodian of texts by MacInnes, and Humphries, who both offer some great insights into all facets of turbocharging. A commonly used phrase in their texts is “pressure differential across the engine”, which encompasses breathing efficiency of the system from manifolding, ports, valve size + timing, turbine size/efficiency/ area/radius ratio, wastegate capacity, and even exhaust system efficiency. The combined opinions and experiences in this thread are pointing to the same issues identified by those authors. Sometimes a smaller A/R may not be detrimental if the engine is intended to run to limited parameters (eg power level and/or rpm), and it has a total transmission gear set/spread to suit the vehicle’s intended use. As frequently put forward in this forum, total area under the torque curve is where it’s at from a best vehicle performance perspective. So we want to get torque up early, and keep it up as long as possible within the engine’s reciprocating design parameters. Changing a couple of variables in the mechanical specs may allow us to juggle where/when torque is produced, but for me the whole show only comes alive when the gas flow through the turbine is enough to spin the compressor hard enough to push the power-producing mass flow into the combustion chambers. Until then it will only work as well as a reasonable naturally aspirated engine. And when the manifold/turbo/wastegate/silencing system reach their capacity then torque (and therefore power) will head on an inevitable decline. Using the GT30 turbine configuration as the basis to keeping this thread on-topic, it seems that the 0.8x A/R offered by both Garrett and HKS offer the best all round characteristic for the RB25. Progressive and reasonably early response down low, and flow-efficient enough to allow the engine to produce good top end without falling over. My 25 with GT3037 Pro S could produce 290rwkW from 6300-7400rpm – fantastic when you consider it would start making good torque @ 2500rpm and start hitting its straps from 3000. Not that different from what we are hearing from others here. Change engine capacity and associated rpm capability, and depending on a few factors a turbine spec change may/may not be worthwhile. The high rev/ torque deficient RB20 would benefit from a 0.6x turbine possibly without hurting its ability to work efficiently up to 8000+rpm. But I think the 0.8x housing may keep compressor speed too slow at low rpm and make it feel really gutless until spinning hard. The RB30/25 combination has engine speed limitations related to useable/available cam specs for that head, and also what conrod and harmonic balancer spec is used. Generally they seem to have done their best by around 6500rpm and make about similar max power as a 25 – say around 400-420rwhp. Their value is in area under the curve – search for the graphs provided by Al and you can see just how potent the cubic capacity is when matched to a GT30 0.8x A/R turbo. Where the use of a 1.0x housing would be useful is if the RB30 engine has enough integrity to rev reliably to 7500rpm and continue to make torque. We are talking RB26 head and some serious valve timing (eg 10.8mm 280 degree cams), forged rods, top quality fasteners, harmonic balancer, 6boost style manifold etc. The whole match is then capable of hitting 500+ rwhp and really requires a turbine that can pass that sort of flow. To my mind the 3076 is more or less redundant then, and bring on a GT3582 with its superior flow capacity. It’s the start of that inevitable cost spiral most modifiers experience. I think Cubes comments really do stand up when looking at total engine spec and application for the 30/25. Maybe for lots of vigourous track use a GT3076 1.0x A/R combination would be worthwhile since higher rpm efficiency is more the focus – pressure differential across the engine becomes a serious consideration and torque production @ 2-3000rpm less the issue. However, the 0.8 A/R housing on a RB25 does help with progressive/tractable response, so maybe Disco has a point about applying the 1.0x housing onto a 3 litre. Delivery is generally more important to me than a dyno sheet number. Staying somewhere near on-thread, the 0.8x A/R housing works very well with both GT3071 and 3076 spec turbos on an RB25. Nobody could complain with either unit if targeting somewhere between 260-300rwkW, but it would be great to drive an example of each to see what was preferable. Flow capacity of the 0.6x housing gave BHDave big dramas when mated to the RB25, but I’d like to see an RB20 punter pick up his setup and run with it – should actually be very good. And at ~ 400rwhp Cubes may be close to the flow capacity of the 0.8x housing. If either he or Al wanted bigger numbers, I’d steer them towards a GT3582 combination. Long post but I had to get it all out. Enjoyable discussion and thanks to Gary.

RB25 has VVT and a front oil feed so head gasket is different to the 26.

Go beyond 9mm lift and there are issues with getting valve springs that can physically fit and do the job without coil bind problems. A good bet is to get the stock head and springs measured up so you have a known base to work from. There are good, useable cams and springs available to suit RB25 heads, but you'd likely need a 26 head if you want to be able to use some serious cams easily.

If running something with a T25/28 flange, do you realise it's in all probability a housing designed to run with a smaller spec T25/28 rotor - and not likely to offer great flow efficiency? Especially with a 0.64 A/R, that combination would tend to limit what happens as rpm and mass flow increases - torque would likely fall away savagely at a particular point as the turbine hits its max capacity and effectively chokes the engine from the exhaust side. Think of it as mechanical constipation. Garrett do offer a slightly larger spec 60mm rotor version GT30 (there'slots of discussion on this forum about it), and the advantage it offers is a much more mass-flow efficient turbine combination. See their catalogue here: http://www.turbobygarrett.com/turbobygarre...T30/GT3071R.htm With regards the cams, I could only offer the opinion that they have to be considered part of the whole engineering package ie. static compression ratio, cams, turbo + manifold. You don't want specs that are not going to complement each other. A set of 4AG cams to suit your application would be only a fraction of the price of your manifold so you'd be mad to not change them. Intercooling is a must, and I see packaging that setup as probably your biggest challenge. Water to air is more complex and probably has a weight penalty, but it can be very efficient at scrubbing temps and offers short-run pipe work between turbo and throttles. Good luck and keep us informed.

I’d think you need to have targets for the operating rev range, and perhaps gearing needs for the change to forced aspiration and the torque curve you’ll see. I agree with previous comments about camshaft specs and static compression ratio ie. get cams that suit turbo application, and keep the C.R. reasonably high to assist overall efficiency. Efficient scavenging via cam and turbine specs should allow an easy 9.5:1 and low pressure differential across the engine to make the target hp. Running to ~9000rpm @ 1 bar is my best guess for 400 crank hp. I agree with Lithium on the 3071, but perhaps the 0.82 A/R might be preferable. You wouldn’t know until you tried both, but I’d say the 0.63 would give a bigger torque hit in the mid range (chassis stability + traction problems?) and stifle the torque production at higher revs due to the turbine mass-flow efficiency difference. The larger A/R size may retain higher rev ceiling (cam spec notwithstanding) and not compromise response if you don’t fall below the boost threshold rpm. And if packaging / budget allows, definitely go with an external gate. The above package might not be exotic, but should work.

Something about the GT28RS doesn't stack up there - Garrett rate them as good for ~ 320 crank hp. I couldn't see them able to pass enough mass-flow to hit on 400 wheel hp. If I was spending the coin particularly on a track car, probably GT30 based turbine in free-floating (external gate) configuration. I'll crunch a couple of numbers and see if I can come up with anything useful.

New head bolts - Nissan genuine. Static comp running cast pistons ~ 8.35:1, so lower than the 9.0:1 advertised for 30E with the 2 valve head. But running in boosted configuration, I felt the higher tension than 30ET would be better. Perhaps a touch higher still at 105-110Nm is not a bad idea for a reliable seal. I'll find out what the ACL tech advice is today.

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.

I wasn't aware of the difference in length, but would nearly think that a longer bolt would require more tension due to extra flex/torsion in the shank. Either way, the higher torque value for the 4 valve head application looks to be the go for me. Any opposing views or experiences?

Looking at available specs, and the instructions on my ACL Race Series MLS gasket I have come across something that's worth asking you engine builders about. Stock RB25 specs require a tightening sequence, with final tension of 93-103Nm Stock RB30 specs require similar sequence, with final tension of 88Nm ACL spec sheet still follows the same sequence, and final tension as per the stock RB30. Difference is that the gasket is listed for fitment with 30ET 2 valve head. I'm leaning towards a final tension of 95-100Nm on the basis that the needs of the 4 valve head are different and requires the extra. Will call the ACL tech help line, but meantime what are the settings commonly used by those of you who've built your own 30DET?

Regardless of the application, various A/R GT30 housings are available from Garrett sellers. You can specify either free-floating (EW), or internally gated. That will get you the T3 footprint, but don't expect it to come cheap.

Gary if you have twin 2" pipes then there is 12% less available cross sectional area for flow vs a single 3" pipe. Muffler design + capacity + noise restriction can also cost significant power if you want to make it liveable and keep out of trouble on the road. I went from 365rwhp to 388rwhp simply from removing a restrictor in the tailpipe that keeps sound levels legal. The change also makes it unbearably noisy for street use, so I can wear the lower output.

It will depend where the thermocouple is placed as to what sort of reading is obtained. Pre-turbine will be significantly higher - you would see up to 150 degC differential across the turbine. Then the further down the dump, and to some extent the angle + depth of intrusion into the gas flow will impact the reading obtained. That said, running @ ~ 12.2:1 AFR @ full load and high rpm on an acceleration run will get me 810-820 degC with the probe placed 100mm post turbine and probe at least 40mm into the pipe.

Start with a full taper tap, and put some grease in the flutes to lubricate your progress. Don't force things overly, and be prepared to back your tap out to make it easier. Remember you are cutting a thread, not just winding the tap in to an existing thread. Also keep an eye on things to make sure your tap is running in plumb. Not that hard.

So is it the -5023 "real" cartridge with a Garrett GT30 turbine housing, or the cartridge running the cropped turbine rotor + OP6 copy turbine housing? Largely an academic question because it's obviously hit the mark for you, but trying to gauge where it all fits with the experiences/results of BHDave and Simon-R32. Let's hope it runs down the strip as you want it to. cheers

Can you give us more data on the 3071, as in whether it runs the full size 60mm turbine, or the cropped 56.5mm version that seems to be used in the hybrid setup with OP6 copy available from various retailers? Just be interesting to compare what you've used vs BHDave and Simon-r32 The on-road results are obviously good, though elevated rail pressures will only stretch the injector capacity so far... be worth testing to see what pressure you are using. cheers

1.6mm (front) / 1.2mm (rear) Overall, the comments by SK and his table steered me towards a conservative approach given it is predominantly a road car and with fairly stock RB30 internals won't be seeing revs over 7000 or for an extended time. Something more competition oriented would probably be better suited to the single 1.5mm restrictor, but I gathered it's all about the combination and its use to determine what way to go. Sump upgraded by ~ 1 litre capacity, increased drain back capacity, and a return to sump catch can should easily keep any issues under control for this application. I feel that lifter bleed-out will be controlled by using oil spec at 10W60 and retaining a second feed will also be a help at start up and cold idle. Should have some idea in a couple of weeks.