3071 Garrett

[Dale FZ1]

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.

[discopotato03]

I have an early copy of Turbochargers by Hugh Macinnes as well , the 6/76 edition .

Some of these old bibles are great reading but don't forget that forced induction went through a revolution in the 1980's with turbochargers creeping into Formula One , Indi Cars and the ferocious rally era eg Group B .

The "pressure balance" is always going to be there with reciprocating popet valved piston engines because they are expected to make usable power over a reasonably wide range .

In an ideal world all engines would have lower exhaust manifold pressure than inlet manifold pressure because that is what would be best at drawing most or preferably ALL of the spent gasses from the cylinders at the end of the exhaust stroke .

If in an NA engine you can develop low enough EMP then the engine will scavange really well - low enough to help draw the cool clean inlet charge into the cylinders in the valve overlap phase . If the inlet system breathes well enough its possible to achieve 100% volumetric efficiency which means the cylinder is fully charged - sort of like if there was nothing on top of the block with the piston at BDC on the inlet stroke . Actually I do remember reading aeons ago about F1 engines reaching something incredible line 120% VE but F1 engines are supposed tro be the pinacle of automotive engineering .

Back to using a radial inflow turbine powered rotary air pump .

You won't get too close to what can be achieved in extreme NA form with turbochargers because of the nossles and turbines in the exhaust tract/s .

A turbine housing by definition is a collector that collects exhaust gasses from all the cylinders and accelerates them into the turbines blades via its nossle/s . This is the place to make or break a turbo engine package because there is a choice of turbine efficiency or the engines volumetric efficiency .

Manufacturers of production vehicles want the turbine to spin up quickly low in the engines rev range because it's early boost thats makes usable torque at "civilised" engine revs .

In the past manufacturers weren't using all the available technologies because they wanted it on the cheap .

Back soon .

[wolverine]

i'm with dale

i have a GT3040 with the 0.82 turbine housing ext gated on the R33.

i wouldn't go down to the 0.63 with a GT3071 or GT3076 based on the positive experience i have with the delivery of the 0.82 with a "slightly too big" 82mm compressor for the street.

the 0.82 is a good thing in my book and with internally gated applications seems like it might be the trouble free way to go.

[BHDave]

I disagree, wolverine. I would not step up to a .82 3071 despite the issues i have had with the .63. I agree on the .82 in your application as if i was stupid enough to consider a .63 on a 3040 i'd neck myself as you may as well get a 3076 in .82 and get better response and the same peak power as a .63 3040

If i had not put the 32 into a wall (stupid act i know) i would have gone an ex gate and .63 non gated housing without hesitation. I was actually looking for manifolds before the crash.

I had more area under the curve and more linear delivery with the same peak power as garys .82. I had torque on demand from 2.5k up and 45rwkw more than gary on the posted dyno sheet at 3500. On a side note, my old plain bearing t300s had more at 3500rpm as well and made 288rwkw (not trying to take away from garys results as i know his transient response would have made for an awesome street car).

This extra timing at the bottom end and scavenging talk is all great, but will you really have more torque with no boost and an extra 3 degrees of timing than you will with 20psi jammed into the engine at the same point? You're optimizing your setup for mid and top end and possibly you will have a wider window where the system is working optimally with the bigger housing, but i do not accept that it is the only way.

It is acceptable to say i want a setup that is optimal from 2.5-5k rather than 4-7.5. Thats the reason i bought a 3071 in .63. I had a setup that made more power but was willing to lose power for response.

The .63 3071 is easy to drive. You don't fall off boost, you don't suddenly have a wave of torque as you are driving out of a corner, and in all honesty it doesn't feel choked in the top end (even with a 7400rpm rev limit). I was as quick at the end of wakefields straight with 255rwkw as i was with 270 odd. IW housing boost issues aside i can't fault the .63 housing on a 3071.

[wolverine]

hi dave

i was mostly talking about internally gated applications given your issues with the garrett housings.

the 0.63 should/does flow plenty for a 71mm compressor.

i naturally defer to your experience with this combo.

[discopotato03]

Just some turbine maps comparing what can be done with the two sizes in GT28BB vs the three for GT30BB turbos .

The two turbochargers I looked at were the GT2871R 52T in 0.86 A/R turbine housing form and the GT3071R in 0.63 A/R form . The corrected mass flow is quite similar and the two compressors are same family just in different trims ie 52 for this 2871R and 56 for the 3071R .

http://www.turbobygarrett.com/turbobygarre...7_1_turbo_e.gif

http://www.turbobygarrett.com/turbobygarre...071R_turb_e.jpg

Not that it's possible to buy a GT28 BB IW turbine housing in T3 flange 0.86 A/R but if you could I think you'd make better power with a GT2871R 48 or 52T than a GT3071R in 0.63 A/R form .

The point I'm making is that small turbine housings are not the best way to get the most from any turbine and if you read into the old bibles they usually say a more modest turbine in a medium to large housing (for that turbine) gives better results .

I look at the power range suggested at the GT3071R page on Garretts site (300-460) as basically telling us what this turbo is capable of given the spred of exhaust gas flow for the three turbine housing sizes .

The real turbo engineers tend to tell you that small AR housings are not flash because they don't have enough volume for the expanding gasses to impart their thermally excited energies into the turbine blades . From memory the term they use is expansion ratio and in a small housing you'd think it would be low .

Anyway this is not getting anyone anywhere . Bottom line is if you want to push a mechanically bog stock engine with this turbo then sure use a 0.63 A/R housing . IMO if you are prepared to go inside the engine and remove some of its physical exhaust restrictions so that it can make more power (and increased exhaust flows) the 82 housing will better deal with the increase in flow ie not become the next restriction downstream .

I also think the 3071R's 56T compressor is too much for a GT30 UHP turbine in a 63 housing , the next sized down turbine (GT28 NS111 in 76T) in an 86 housing gives about the same flow and people don't complain about how GTRS's (2871R 52T) work on RB25's - would be even better in a 0.86 A/R housing .

Anyhow I've been there before with the GT2860RS 0.86 A/R on a 2L four and it was really good .

A .

Edited November 11, 2008 by discopotato03

[Dale FZ1]

This extra timing at the bottom end and scavenging talk is all great, but will you really have more torque with no boost and an extra 3 degrees of timing than you will with 20psi jammed into the engine at the same point? You're optimizing your setup for mid and top end and possibly you will have a wider window where the system is working optimally with the bigger housing, but i do not accept that it is the only way.

It is acceptable to say i want a setup that is optimal from 2.5-5k rather than 4-7.5. Thats the reason i bought a 3071 in .63. I had a setup that made more power but was willing to lose power for response.

The .63 3071 is easy to drive. You don't fall off boost, you don't suddenly have a wave of torque as you are driving out of a corner, and in all honesty it doesn't feel choked in the top end (even with a 7400rpm rev limit). I was as quick at the end of wakefields straight with 255rwkw as i was with 270 odd. IW housing boost issues aside i can't fault the .63 housing on a 3071.

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

Edited November 11, 2008 by Dale FZ1

[wolverine]

i am happy to be sponsored by Garrett, using their R&D budget check it all out....

[discopotato03]

The thing is that the waste gate is regulated by boost pressure not exhaust manifold pressure and a waste gate would only begin to regulate gas speed once the target boost pressure was approached .

I can see scenerios where people could put an 18-20 pound spring in a big external wastegate and wonder why the turbine inlet pressure went stratospheric . It's because until the gate cracks open (signalled by boost pressure only) it achieves SFA so not a very effective exhaust manifold pressure relief valve .

Corky mentions exhaust pressure signals to operate wastegates and I think he even said don't laugh because it's not as silly as it sounds . If you did this with an exhaust side restricted turbocharger the rise into boost would be pretty lazy dependant on what spring load the gate had .

If a turbocharger is properly sized let the wastegate regulate air pressure and the lack of restriction regulate exhaust gas pressure .

Most diseasel turbochargers are big on the hot side and not so much on the cold side , they do this because they want low turbine inlet pressure and don't need huge compressors (in comparison to their turbines) to make their peak power .

Atmittedly their CR's are pretty high and they make reasonable torque at very low revs .

A .

[Dale FZ1]

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

[Cubes]

Lithium went from the .6 rear to the .82 IW and loves it.

Might drop him a PM so he can post his comparison.

[BHDave]

damn work connection not allowing me to properly access the page today.

Some good reading.

I've said in a few of the other 3071 threads that if you want a 3071 in IW then do not under any circumstance get a .63 so in that regard i agree completely with Dale. And i am also interested to hear a back to back on the turbine housing differences in the same car. Any idea on what the car is primarily used for?

[discopotato03]

I reckon if I was doing a 3071R now I'd be asking Brett to grab a GT2871R 52T and swap in a GT30 turbine and bolt the 82 IW turbine housing over the end of it .

A bit more compact with the T04B compressor housing , a bit more responsive with the 52T compressor and low pressure with the 82 housing .

Not the cheapest option nor an off the shelf one .

A .

[Dale FZ1]

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.

Edited November 12, 2008 by Dale FZ1

[discopotato03]

It's not real hard to do , whip off the comp housing and jamb nut and pull the turbine out . Replace with a GT30 one , balance it and bolt on the GT30 housing .

Whenever I asked he said you're only paying for one turbo just not sure if he's charging for the balance .

The T04B comp housing is a bit smaller than the T04E one so probably won't need the spacer to get the comp housing off the exhaust manifold .

http://www.turbobygarrett.com/turbobygarre...R_472560_15.htm

http://www.turbobygarrett.com/turbobygarre...071R_turb_e.jpg

Edited November 12, 2008 by discopotato03

[Dale FZ1]

Whenever I asked he said you're only paying for one turbo just not sure if he's charging for the balance .

The T04B comp housing is a bit smaller than the T04E one so probably won't need the spacer to get the comp housing off the exhaust manifold .

Definitely the mechanical process of changing components isn't difficult. And if your preferred supplier is prepared to wear the cost of carrying the cost of surplus parts from the build then it sounds like you're onto a win-win case. My concern would be as consumer having to wear the cost of a complete turbo + GT30 rotor + housing + rebalance.

Bear in mind that with the shift to physically smaller TO4B syle comp cover it probably won't shift the top end mass-flow as easily as the T04E, but eliminating the need for a turbine spacer would be a positive.

If you're serious I want to see pictures of this unit being built and installed, and most importantly given a comprehensive rundown on how it goes on your 33. I'd even fly down from Queensland to see for myself if invited. Keep us updated because this could be an interesting variation on the 3071 spec. I have to say it appears an odd mix, and wonder why HKS with their specialty mix/match range for the Skyline didn't make something similar.

cheers

Edited November 12, 2008 by Dale FZ1

[discopotato03]

It would just look like a std IW GT3071R but with the B cover on it , in fact if you used the B housing and adapter ring off a GT2871R 56T it would all bolt togeter with factory parts and no cartridge alterations .

Thinking about it you could vew this 2nd variation as a scaled down XR6T style GT3582R - because they use the next size down comp housing ie T04E instead of the usual T04S .

Don't quote me but I seem to remember reading about B covers on 3071R's I think on EJ turbo engines . Most Rex engines (all single scroll ones) have a dogs breakfast header system and it can make healthy turbos laggy on them , possibly the smaller housing brings the air speed up a little faster for a given flow rate and helps pull the bottom end up .

As per HKS , they DID have 52 and 48T compressor options on 2835's and 3037's - just not in their Pro S turbos . What both types of Pro S's did get was a custom port shrouded comp housing and that makes a difference if the comp trim is big and the turbine housing A/R is a bit limited . The full height compressor blades can cycle air out the ports so unload the wheel a little and not over feed the engine to the point of surge .

Cost would come ito it too .

The possibilities .

[skylinecouple]

What I'd like to know is, is this really all my compressor has. I have a feeling that because the larger housing is so efficient at removing exhaust gas it is also making the comp unable to flow enough air. Does anyone think it strange that no matter how hard I wind the boost over 18lbs it will not make any more power ? Ok, now I have a non laggy crisp loves to rev combination, but, what if I change cams and nothing. What if I redo the whole exhaust to 3.5" and it simply won't flow any more. Should I have got the 3076 ? Would it be any laggier ? Questions questions. Time to live up to my own motto, suck it and see. ( no not the homo type suck, that's just rude).

Oh, and another question, Should I just get a cam wheel and try that first ? I think it strange that I can still feel the revs slowing down around 5,700rpm. Feels like there's more there but the motor can't process it. These turbos are running 22lbs elsewhere so how do I increase my efficientcy ? What's more important, bearing in mind the turbo combination, is it the intake or exhaust cam. Do I need to evacuate the exhaust better or get more air in ?

[Dale FZ1]

During my initial evaluation of the compressor map for your 3071, I felt that the compressor was not likely to do better than ~ 260-265rwkW on a mechanically stock RB25. (ie. no cams/porting). To be honest I still have that opinion, but can wear a plus/minus 5kW variance. Using the similar but different HKS 2835 Pro S there have been exceptions claiming up to ~ 290 but I don't reckon that was representative of the breed.

Remembering that phrase pressure differential across the engine and what it entails might give a guide where to look for further improvement. Now if it feels like it is nosing over somewhere around 6000rpm there is sign of a restriction that may be causing torque to drop off prematurely. As I commented about my 3037 Pro S setup, it held maximum power for over 1000rpm - a good outcome in my books. Yours should be able to do something similar.

Checking back through your thread, it is possible that the exhaust system is responsible for a post-turbine restriction that effectively causes a raised pressure differential across the engine. More boost then does not equal more mass-flow, and hence the power noses over. Assuming I'm right, if that restriction is dropped then you should find the torque @ 6000rpm plus does not fall away as quickly, and your power output will climb. example: Pulling out the removable baffle in my system gives a 23rwhp gain without any tuning changes. But in that instance the noise gain is intolerable for the road.

I'd reckon that is the first place to check, although cams are definitely part of the equation if chasing higher levels of system efficiency. Examine your dump design and diameter up to the cat, and consider the muffler configuration.

Edited November 13, 2008 by Dale FZ1

[BHDave]

I agree with dale on that one. My power goal with the 3071 was always pegged at a max of 270-275. I just don't think the compressor can do more based on what i have seen on both 2835s and gtrs/2871's

For reference, my power was still rising at 6k, even though boost dropped off to 1 bar.

If you're interested you can have my old split dump for a case of beer. It will need modification to fit but still cheaper than a new one and certainly better than an exhaust shop one.

I also found big gains by opening up the exhaust post cat.