Dale FZ1

Thanks Darren the max power number is very commendable. Shame that it is scaled in road speed, not engine speed. Can you add to the discussion with regards to delivery, and how it compares to your new setup? (from memory you went to the 3076?)

Hi Adrian Well here's a punchy, responsive 300rwhp from my GT2871R 48T highflow @ 13psi: That unit on an internally stock engine is particularly responsive, and progressive in its delivery. Max power is developed @ 6400rpm, so the useable rpm range is same as factory and the gearing is suitable for the delivery in a road application. It's worth pointing out that my (and your targeted) power level (~225kW) is some way below the 260 odd kW that was the target in the original thread query about the GT3071. As per many discussions about upgrades, the individual has to set a clear target on power, and understand how certain specs can/will/do impact on delivery. My view is that with the GT30 based turbines applied to a RB25 the useable engine rpm range general shifts upwards by 500 or 1000, or maybe more. So it becomes an exercise in choosing the optimum compressor spec that can cope with that shift and still give good results. While the GT3071 may deliver 240 or 250rwkW, I remain out on the limb and say that the quicker responding GT28 based turbine will eat it for bottom end response, and with the 56T GT2871R core still deliver the same/similar top end numbers. For me it makes it hard to put together a compelling argument for the GT3071 into a road application in that instance. Move into the GT30 range with the option of 71 or 76mm comp, and again I feel that though their response capabilities may vary, it will be by a small margin of little practical consequence. That difference may be tailored by the use of either the 7 blade TO4S compressor or the 6 blader and the different pumping characteristics they have. But it is worth considering that either spec offers bigger flow than the 71mm and won't drop off at higher engine speeds. When you consider that the useable maximum engine speeds are going to be up by 500-1000rpm, that is an important aspect in making the choice. For me then, it's like drawing a line in the sand and deciding which side to stay on: stock engine speed range and moderate power, or elevated engine speed range and higher power. With the higher power option, it is still possible to have a satisfactory bottom end delivery but not likely to equal the lower powered, smaller spec GT28 unit(s) that I've alluded to. They payoff comes in that lesser restricted high end flow. It's interesting that your US contact has reported those results, but we are ignorant of just what internal engine changes have been made to yield numbers like that. It's also on a different capacity 4cylinder. The use of the descriptor "wildcat" with the GT3071 is probably very apt - it's often used in shooting with special modified rounds intended to fill some small niche. As you've indicated, it seems to need things "just so" to suit it. When applied to a RB25 I'd think it means either accepting its shortfalls with a stock engine, or effort and expense to make it work. The logical options within financial boundaries seem to be either run with the smaller 2871 units, or the bigger 3076 units and reap either better response or more power. FWIW, I do believe we're generally on the same page but it's important to stay on-task with the original query about an RB25 application. 300hp is a lot different from 350+. I also happen to believe that your target of 300hp is about as high a useable (stress that word) amount as can be applied to a road car if you want it to get to the ground. Check below - that looks impressive, feels great, but it was one of the slowest cars at that event on that day.

The effect is understandable, but as per your first post, I think we are on the same page viz. appropriate speed ranges for the 71mm compressor. I think that the GT30 may just flow a little too freely compared to a GT28 based unit, so inhibiting the ability to accelerate the 71mm compressor up to speed where it is pushing appreciable air mass (ie. generating boost). Sure, the free flow promotes much less top end bottling of exhaust, and lets the compressor run to its maximum capacity more easily; but I'd suggest that there may be more overall advantage in teaming the GT30 turbine with a 76mm compressor in some specification. I'd predict the result as having negligible difference in perceptible response or lag, but with the capacity to generate more torque at higher engine speed while equalling the 71mm down low. If costs involved in the install are the same, it makes for an easy choice. For the speed range and capacity of the 71mm compressor, I'd be inclined to match it with the smaller GT28 spec turbine even if it means using a stock/modified Nissan housing. I agree that the GT3071 is something of a wildcat and therefore difficult to pigeonhole within the performance spectrum. That comment applies equally whether the 71mm compressor is teamed with the 60mm turbine, or its cropped 56.5mm brother. So it becomes more an issue of identifying where abouts in the power:response equation your performance needs are and then choose accordingly. Hopefully this discussion will prompt some comment from someone who has driven/tuned engines with the types of turbo being discussed. Hope that clears the air, and kept topic on track.

Trying to keep the original thread on-track, I'd suggest that the 3071 is more of a compromised unit in terms of balanced power:response than either the 6 or 7 bladed 76mm compressor options available when mated with the GT30 turbine. I'd suggest that it just doesn't have the pumping capacity up top to make big (>250rwkW) streetable power, and the GT30 probably flows a bit too well to get it pumping early. Progressive and driveable - yes to a point; but I think the 71mm GT35 compressor is better served with a higher speed GT28 based turbine from a street car perspective. You may lose 10kw off the peak power number but gain appreciably better response down lower. If higher power is the target I'd say the GT3076 is the most logical choice. To Cubes: I'd think the GT3076 will do all that you want, especially with the 3 litre engine capacity. I also reckon that using that gearing will do wonders for performance within streetable speed ranges. In many ways the relative merits and characteristics of the 6 or 7 blade 76mm compressor is something to get your head around. One will offer more low down pumping capacity (7 blade), while the other will offer more high speed capacity and efficiency (6 blade). Neither is inherently "bad" or "better", but they are different.

Well I'll step out on a limb and say that while the GT3071 should (with the right selection of supporting external hardware and good tuning) be able to support somewhere in the vicinity of 250-255rwkW, the boost and engine response available from certain 76mm compressor combinations should have little appreciable difference in response as Lithium has alluded to. The 7 blade T04S style impeller has been lambasted in many threads as being old-tech, but it does offer a large amount of air-moving capacity at lower turbine speeds. With the right turbine, that means it can respond ok, even if it won't have the high speed efficiency and power capacity of the 6 blade impeller. It would be worth researching and finding what users of that actual combination have to say. There is one SAU member who has run both 6 and 7 blade compressors that I'm aware of. I'm not saying to go one way or the other, merely to search before deciding.

It's not so much about the power numbers but the response with running an engine spec like this. Run with an intelligent tune there is no reason why it wouldn't/couldn't be reliable, possibly more economical, and with the sort of power that works well on the street. That said, do we have any dyno sheets of any description? Here's a graph of my RB25DET running 12psi to achieve 300hp. It's not overpowering, but very useful and responsive. The dip right at the top end is from pulling ignition to combat knock. I've considered that a well thought-out DE-spec engine with similar power numbers would be even nicer, response wise on the street. Perhaps water-meth is the key to making one detonation proof?

I run a stainless mesh filter, with a K&N Filtercharger sock. Looks pretty much like a shower cap. Flow performance is great, though in dusty conditions (grass/dirt motorkhana) the fine dust has shown signs of passing through the filter. Slightly off track, but has anyone using a K&N ever reported an AFM failure due to contamination of the hot wire by the K&N oil?

Top work Glen The pictures tell a lot. Given the choice would you do the install with engine in the car, or on the bench? What spec were those cams? Looks like lift is very little different from standard, but the more rounded egg shape on the lobe points to a lot longer duration than stock. Makes it easy to see why/where they are different. **edit** should have looked at the markings on the box 256deg 8.5mm lift Any commentary to include about things to watch out for? cheers Dale

Don't have anything for sale, but happy reading here: http://www.turbobygarrett.com/turbobygarre...bo_tech101.html Here's also a starter on the differences between RB20 and 25: It is worthwhile getting your hands on one just to check it over, and the two things I've learned is 1. biggest is not always best 2. more (impeller blades) can be better If you have a technical bent, then it is a fascinating area of study in engineering. People talk about this trim, or that A/R, or that major diameter, sometimes without realising that it is a difference of less than 6mm and yet it can make a difference of 100hp and seconds of lag. cheers

One of the best technical threads I've seen. Top marks for finding it, and thank you for sharing. I noted the opinion that while there are undoubted benefits from using WI, there is a point below which the expense makes it not worthwhile - provided all the conventional bolt ons and tuning is already in place. What I really enjoyed was the attempt to enlighten us on how water is actually involved in the chemical processes of combustion, rather than being present but uninvolved. cheers

I'd agree there is a good chance of failure if he's wanting to run it at 14. I wasn't prepared to run mine any higher than stock, knowing that elevated speeds would eventually result in the turbine rotor parting company with the shaft. Slide's product would be a useful upgrade, but quite frankly a useless change unless the ECU is able to support it. And it seems that the ECU currently won't handle the mass air flow capacity of a stock turbo @ 14psi. It's not a case of the AFM "maxing out" though, just exceeding tuner defined parameters within the ECU settings at those lower engine speed ranges.

Compressor surge has nothing to do with an electronic tune. It is about the physical inability of the engine to ingest the mass of air that the compressor is delivering. It is generally associated with big compressors and small capacity engines running a bit of boost. Garrett offers a really informative tutorial here http://www.turbobygarrett.com/turbobygarre...bo_tech103.html to explain the phenomenon. Original post indicated a stock turbo, running higher than stock boost. Very very unlikely to be surge @ 14psi.

How about failsafe? Maybe they've retained/modified some of the protection parameters. The AFM reports flow voltages in excess of what is deemed "safe" by the tuners, pushing into map cells that they say it shouldn't do if operating at a certain boost level. Then it just goes through a series of rich/retard steps to discourage the driver. Guys running stock ECU report the same phenomenon but generally at lower boost.

The benefits from using the water/alcohol mixture vs 100% water to me are questionable when/if you weigh up the logistics of buying, storing and mixing the brew at consistently the same blend. Personally I'd steer towards 100% water - 20 litres of distilled water isn't costly, difficult to obtain, or offer any difficulties in storage. Having said that, I'm not to argue whether there is a performance advantage one way or the other. Whatever the case, or the % blend, you can be assured though that if you inject a 50:50 mix then it will still enter the combustion chamber in the same proportions. The principle of heat transfer to the atomised spray works the same regardless of whether it's pure water or a mix, so all that happens is you have water and alcohol drawn/forced into the combustion chamber that has been converted to gaseous form. It's the conversion that drops the charge temp. The chemists amongst us can inform which of the two has the greatest latent heat value, but there is obviously a limit to the amount of water or water/meth that is optimal for a given engine. And depending on the mix, that may vary. All pretty straightforward application of science that I recall from senior school days. My general understanding is that these vapours do indeed affect the rate of flame front propagation, slowing it down in similar fashion to using high octance racing fuels. So you've got the double whammy of cooler charge and extra knock resistance which allows more advance. Yep, water injection was used/developed in WW2 piston engine driven planes as was various types of forced aspiration to help them get off the ground quickly, and operate at high altitude (in particular). There were a few cluey blokes around well before we came into being.

Showing my ignorance, but what is a Central 20 ECU? Sounds a bit like electronic intervention to me.

N15 = 6000rpm. The scale is in 400rpm increments. I didn't know what to expect with the AFM until I checked the logs. From memory when running stock turbo + boost I hit max voltage @ >6000rpm with 223 rwhp. Torque delivery (ie sudden sign-in) and quantity combined will determine what the clutch can withstand. I've been lucky to date, but expected to have to budget for a replacement. It is definitely useable and accessible power, though the nose-over beyond 6000rpm may not be to everyone's liking. Doesn't bother me - there is plenty of torque easily on tap when you pick another gear. More in a few days.

Still very much a work in progress. Yes, it's fairly brisk but not mind-blowing. No idea or interest in seeing what it will do at a drag strip, but it covers ground quickly without feeling overwhelming. I aimed for smooth progressive power, which it has. Still running the stock clutch, with no signs of slippage. A larger trim unit would probably be more sudden in its delivery and harder on the clutch. I've acquired a 14psi actuator, which will be fitted tomorrow to cure the 2psi oscillating drop from 14-12psi that was logged on the dyno runs. Between better/more accurate boost control, slightly less rich top end fuel, and playing with the exhaust cam timing I expect to see a slight power lift. I will update the thread after dyno later this week or early next. Here's what my logged duty cycles look like: That is using the S15 injectors. Stock fuel pump could not keep up the flow and AFR started to lean out at the higher rpm. The stock AFM really is marginal, and clearly hits max voltage output @ 5115mv. With extensive data logging of AFR and tight fuel control I think I can get away without it at this power level.

Agreed. If you've got R33 spec housings, I would suggest using the 56T 2871 core. It will provide the airflow required to make 240 (not too hard) - 250 (a bit harder), without the risk of surge. My full load ignition timing is at 24 degrees up to 4000, then drops-rises-drops -2, +2, -1 in the remaining range up to 6800. If your base settings are right, then you are missing out on a lot of power if you have 15 deg at full load. With your budget I'd be aiming for the cams specifically to make the power without having to use high boost levels. And yeah, the more urgent exhaust note is an added bonus.

Michael, you're using a water/meth mix though - correct?

Well my high flow has the smallest trim 48T 2871 core fitted. Still made 295hp (219kW) @ 14psi which dropped to 12psi by max power rpm. There is marginal scope for improvement, but plots show that it will quickly head into choke as you've described if I try to push it beyond 15psi. I have a 14psi actuator going on, and will be happy with whatever it yields. So yours should be capable of at least similar - do you know if your ignition timing was really conservative - it was amazing to see the power numbers rise as the ignition was progressively advanced over consecutive runs RB20 and R33-spec RB25 turbine housings and impellers are the same size. If going for something high flowed for the Neo motor, you would be mad to use anything other than the OP6 turbine housing. Bigger flow + deeper breathing through the improved variable cam timing setup will give the potential for both a better mid range and higher top end. Do a search on high flows for jmac - he got some pretty tidy results on a R34 last year. Try around 250kW @ 16psi or so. Alternatively with 3G to spend, I'd consider a Slide unit + cams and still come in well under.

Total agreement about the need to use wideband to tune. Regards the effect on AFR, can I refer you to my earlier post about the impact on my mate's rally car during tuning? Going from 11.8 to 12.9 is quite significant. Note: that particular system used only water injection - no intercooler. When tuning "around" the water injection, did you play mostly with fuel, or ignition? cheers

To the original topic of the thread. If I was going down the upgrade path again, I would probably look for a good quality SMIC to control pressure drop at higher boost, and avoid having to cut bar work to make a FMIC fit. Then I'd also include a water/meth kit. Overall cost would probably end up in the same bracket as using a good FMIC, but the results of the water/meth kit superior. The question would be can you live with checking/filling the reservoir on a regular basis?

Perhaps with a methanol mix, that is right. Obviously the meth combusts, which would skew the results vs using only water. I'm not going to contradict the observed experiences of guys who have used/tuned with it. Two different approaches altogether, and would require you to use either one (100% water), or the other (water/alcohol mix) and stick with it religiously. A friend of mine having his rally car tuned last week found that the AFR leaned off from 11.8 to 12.9 using 100% water.

Cubes I think you'd find the AFR would become leaner due to the increased density of the cooler intake charge. Therefore you'd want to add fuel. The slower burn rate should allow more advance to be wound in as you say.

Serious question Brett? The concept of using water injection involves adding the fine mist to a hot intake charge, and the water absorbs the heat energy to convert to a gas (steam), thereby cooling the intake charge. More dense intake charge then allows tuning to make the power. Obviously there are benefits that adding a certain % methanol to the mix brings, but note people do not use 100% methanol. Water will accept/mix the alcohol but only to a certain extent. I'm aware of some of the properties of nitromethane, but who in their right mind would try using that in a water injection setup? The risk of fire amongst other things is just a little high, and I'd be dubious how stable that commercial mixture is - ie. how fast would you have to use it once opened? cheers Dale