Lithium

Just had a squiz at tune and logs over brekky but don't have a lot of time for yarning. Still mostly head scratching but things I felt compelled to mention: It's been ages since I've tuned a pump gas RB25 but I'm pretty sure the timing looks a bit soft, not necessarily crazy soft but enough that if my memory serves correctly - RB25s I've tuned (and others I've seen tunes for) would lose noticeable power if your timing map was applied to them. Not saying as a criticism, but an observation. The tuner could have either been competing with knock, or generally "not confident in the setup", but one way or another that alone could explain some of the lower power at the top end. There clearly is stuff going on, I'm not pointing at timing as possibly being the problem - just added that to the discussion. Also, you aren't logging turbine speed... do you have a sensor or was there just one used for tuning? And what gear were you accelerating in with those logs? It didn't look THAT bad lag wise, and looking at the datalog from the dyno - most dyno operators I know of let the engine accelerate at 500-600rpm/s for a dyno sweep but your tuner has run it WOT from 2000rpm to 6000rpm in ~4 seconds, or almost 1000rpm/s. When you consider the "action zone" for boost threshold is 2500-4000, yours is given about 1.5s to build target boost when most RB25 dyno plots you'd be comparing with may well be given closer to 3 seconds. A good part of double the time to hit target boost in that rev range makes a difference, and may account for a bit of the less spool... if it's driving quite nicely then maybe the "lag" could be a red herring, though I could be overestimating this difference. I personally do most of my tuning in the 5xxrpm/s range so that's what I use to build expectations of spool. You could try giving it beans from low rpm in 3rd or even 4th gear to get a solid picture of the actual boost threshold.

Here we go, this car "upgraded" from Precision Gen2 7675s to Xona Rotor 10569S (the previous generation 72mm compressors) using a reverse rotation turbo for one side and here is the video for how they found that: This car has just upgraded to the new XR7169S (also mirrored) which goes from being 105lb/min with a 99mm exducer to >120lb/min with a 92mm exducer, and so far have proven to be MUCH more potent than what this R8 was running at the time of the clip but no cost to spool. Out of interest that car is supposedly the quickest 60-130mph "street car" in the world according to Dragy results from when it had the old 72mm Xonas:

I would say it's a case of when, not if the echo (Xona term for that kind of thing) versions come out of the new ones

Oops I meant to link them: XRE7169S Ball Bearing Turbocharger – Forced Performance Similar area to the equivalent Precision

Instead of starting a new topic I'm going to revive this zombie. Forced Performance/Xona Rotor have started releasing turbos based off their latest range of compressor wheels, the "XRE" range and so far they are looking like the ducks nuts. As people who've been around a while would know, I've generally liked what FP do and been pretty excited about their UHF turbines but haven't pushed the idea *that* hard in the RB world as there have been theories and murmerings I've heard which have had me not 100% confident of how well they'd work on this platform. At face value everything sounds perfect, the turbines are low inertia, have very low back pressure, and their compressors had decent flow for their size... but unfortunately there is more to the picture. This isn't gospel persay, just me extrapolating and theorising - though it's not all completely unfounded and I'm just painting a picture of why the previous generation may not really reflect on what we should expect with the new ones. The HTZ compressors used on the Xonas ALSO like higher pressure ratios to do their flow, and the UHF turbine wheels seem to like to operate at higher rpm to generate shaft torque. This essentially ended up meaning the Xonas only really suited RB/2J engines when using larger exducers (94mm+) but those exducers kept the rpm down on the 69S turbine that on paper also suited best, meaning they potentially struggled to drive the larger compressor as well as you'd hope. Instead of high EMAP, there was the risk of more lag than you'd hope and actually "running out of turbine" in terms of not actually having enough shaft torque to drive the compressor fast enough to make the numbers. This could potentially end up with people undersizing and overspeeding their compressors on larger engines to try and make the numbers they were looking for - and essentially "look" like they were getting away with it because the crazy not-restrictive UHF turbine stiiilll didn't get up generating massive back pressure. Not ideal, but this is how some went forward. Bring on the new releases (so far), the XRE6869S and the XRE7169S - running a 88mm and a 92mm exducer respectively, both in that mid 80-mid 90mm exducer range that seemed to compliment the 69S turbine very very well, but *also* pumping a crapload of air for their size. A lot of the magic I expect to start showing up when people use these will probably be attributed to the new compressor aero but I think the MUCH better match between compressor and turbine behaviour will make the gains way way better than expected, and start actually showing the magic the UHF turbines should have already had the potential for - just hadn't got the right pump for the job. The XRE6869S: This is a 68mm inducer compressor capable of 105lb/min of airflow max, paired up with a low inertia turbine. Picture something capable of 1000hp @ hubs on E85 with good spool and lower inertia than most things capable of this kind of power. The Xona 68mm turbos have already been known to be better underfoot and lower EMAP than their key opposition, but the old 68mm/94mm 95lb/min compressor was maybe not quite up to the task of a complete takeover in that "68mm turbo for street use" zone. The new 68/88 105lb/min jobby on the other hand, should be very interesting. Unsurprisingly they've been proven to outspool and significantly outflow the old XR9569S which were already beasts. The XRE7169S: This is something that could be VERY interesting to see on an RB. I know of these replacing PTE7275s (and in one case even twin 7675s) and matching or improving their power but MASSIVELY improving power delivery. They are already proven to be absolute monsters for their size, talking 1100-1200hp @ hubs on ethanol and beyond that on methanol on full send - but without the "Big frame" power delivery of most things capable of these power levels. The nuts thing with these is you can literally get both turbos on what is essentially a GT3582R style frame, T3 flanged etc. There will be a slight cost to compressor flow with the old GT3582R style compressor cover footprint but not THAT much. There have been posts in this forum where people have antagonised about whether to go with a 6870 vs 7275 or jumping from a EFR9180 to a 9280 vs jumping to another brand and losing a tonne of response - when talking about drifting into that 1000hp+ mark but still being a bit shy of turning the car into something that behaves completely like a drag car. These guys may make that compromise much less so much of one.

Nah I was more checking whether E85 or petrol, which makes a big difference. Ok Mainline hub, that shouldn't be THAT low reading. I would have expected this to be sufficient for what you're trying to do Yeah this seems the wisest at this point, if you are able to get more data to scrutinize then that MAY build a better picture. At this point I don't think I'll add too much until some data is available to try and build a better picture of what might be going on unless you have any other specific questions? In terms of turbo match you shouldn't be far off with what you have imho, an EFR7163 (with a bigger hotside) would be a nicer match probably, and some more modern things like Garrett G-series may be a better balance for a bigger engine but at this stage while the turbo match may not be OPTIMAL... I suspect there is something not performing as well as it should be in the setup. <250kw @ hubs on 98 isn't right.

You are FAR from the first person to overlook this. I've been in this club, though learned from it some time ago Very loose plotting of a generic "2.5 single turbo" on pump gas against an EFR7064, adding in compressor efficiency (and taking a random guess for the off the map one) and then adjusting the turbine expansion stuff to suit and it definitely paints a picture of excessive EMAP partly aggrevated by running off the comp map: https://www.borgwarner.com/go/CRTINK While still being unsure whether to treat this if it's an ethanol or pump gas / 98RON setup - did the tuner mention knock being an issue?

Well shoot. Thanks! My walls of text may get a bit less painful now

Haha the numbering thing is making things a lot easier to follow - I miss the days when it was easy to just quote selective bits of a post to make context easier to follow. 1) Ok interesting, I'm used to seeing stock plenum setups fall over earlier. Not going to question it if its stock, though you can run aftermarket plenums with stock throttle body fine. I wasn't saying it NEEDED to happen, there is definitely a sacrifice down low if you go a FFP and I'm at this stage definitely not saying its a thing you need here - just breaking down all the bits of what is going on as often there isn't "just one thing" if you're not getting the power curve you were expecting. 2) MAP is absolute pressure, so strictly speaking yes - 18psi + ambient pressure, so 32-33psi area absolute or ~18psi boost/gauge pressure to redline is what you're looking for. 3) Be interesting to know whatever further data you can get from logs but it DOES sound like you guys have been pretty thorough with boost leak testing 4) I would expect better spool than what is coming across on that dyno plot, from memory we saw around 300rwkw on a hub dyno with the .83 IWG on stock exhaust manifold, freddy FFP, BP98 RB25 on a Dynapack hub dyno. What fuel are you running, and is it a Mainline rolling road you're being tuned on? If so, that probably translates to about 260-270rwkw, and we WERE initially stuck at around 260kw when we had wastegate control problems (flapper being blown open). 5) I probably asked a redundant question here, sorry... I missed the point where you said there was no significant pressure drop across the TB. If that is the case at max rpm then this is very unlikely an area to be worrying about. In regards to the bonus round questions, we initially tried to be clever and fit a two port actuator with lower base pressure to the EFR and that didn't seem to be "enough" - I guess in hindsight the fact that we were still using a 3port solenoid and the fact it was clearly mostly back pressure causing the issue this was not the way. The problem was solved in that situation by just going to a much stiffer spring/actuator. In terms of what I'd have suggested, can you confirm the fuel and dyno (rolling road?) that you're using? And this is for 280-300kw with nice driveability?

Sorry, got no notification of the mention and just happened to stroll in for a nosy around while having lunch - will be brief (for me :D) because I don't have heaps of time right now but reading through all the comments, I'll address things I haven't noticed specifically mentioned yet: 1) This won't in itself cause enough of a problem to "be the problem" but it's worth mentioning that I'm *pretty sure* that the 3076 dyno plot in the comparison will not be running a factory plenum. I think people forget or don't even realise how much of a different the typical GReddy-esque plenum makes on power delivery and the resulting power-per-psi you can make. Stock plenum falls over much earlier in my experience. 2) Can we confirm that it is DEFINITELY holding a full 18psi to redline? There is mention of WGDC increasing to maintain it, but how often I see comments that something is tuned for xpsi and the curve actually drops off towards the end. I've had experience with an EFR7064 and they work decent enough on an RB25, not the "best" at all these days but you should definitely be able to get a better result than this. The one I was involved with ran a .83a/r open T3 IWG setup and took a lot of pissing around to stop the flapper blowing open, which depending on what the boost curve is doing could cover some of the WGDC going to the moon. The EMAP may not even be THAT bad, just the BW actuator setup doesn't necessarily play nice. Even dropping a couple of psi as the rpm increase could really put a damper on the curve. 3) In terms of using "it's not at max rpm" to confirm its not got a boost leak or anything like that, not necessarily a rock solid method with a 7064 which is more of a "I want high pressure ratios" turbo. At a PR ~2.2-2.3 (for 18psi at sealevel) we're looking at 120,000rpm *MAX* if you're staying within the happy-enough working area of the compressor. I treat anything <60% compressor efficiency as a point where the efficiency of everything starts becoming noticeably worse, EMAP starts ramping up more aggressively etc. If you were at 130,000rpm for sake of argument, and assuming you're in a pretty happy place because 153,000rpm is meant to be the "speed limit" then unfortunately it's a trap a lot of people have fallen into with EFRs. This combo SHOULDN'T be off the map there, at least that badly, so if you are 120,000+rpm then I'd not rule out pressure testing the boost system. Probably still wouldn't hurt if it hasn't been done. 4) In terms of your turbine wheel observation @Kinkstaah - it's a trap. The Borg wheel aero make them not comparable size vs size with Garrett ones, the EFR7064 turbine wheel flows a fair bit worse than a GT30 imho/experience. Also spools better, though. Which brings me to another observation, the dyno plot looks laggier than the T3 .83 EFR7064 a mate has on his RB25 which could be a hint. Maybe. 5) I'm not assuming your tuner (or anyone else) is useless - their investigation and frankness actually is pretty encouraging but I always feel obliged to mention *ANY* thought I have as its always worth ruling everything out. Are you 100% sure the e-throttle is physically at max WOT? This doesn't look outrageously unlike a part throttle "turbo" dyno pull, both in shape of the curve and also the data you're reporting back. Plenty of people who aren't the dumbest have missed things like this (like me) and it can be worth ruling stuff like this out when there are no other clear smoking guns. I gotta scuttle off now, but those are some "obvious" things that jumped into my head that I haven't seen mention of.

Yeah makes sense to a degree, like you have a "strong" 3.2litre engine anyway. As soon as it starts getting any boost the displacement advantage gets compounded and you start picking up speed (and with that, rpm) quicker than the poor beggers with 2.6s and even 2.8s. As soon as you get it up and cooking its going to be insane, but its only going to be useful in races you're allow to get up on launch control or at least involve very illegal speeds on the road but you were already there with the 76mm.

I was reading through the post and the comments and was basically going to say something along these lines - feels like you answered your own question really I haven't had direct experience with the exact kind of setup you are talking about here, but my observations and involvement with things of this level basically surmounts to - once you are talking about 80mm+ turbos on "small" engines the lag etc all becomes a bit academic. You are going to NEED launch/rolling start antilag, you're going to need to rev the hell out of it and a fast shifting trans with shift cuts are ideal if you want to keep progress happening well. At this point if you want more power and you have an option, the only thing to think hard about is "Do I have the trans, fuel system, and engine spec to ensure I can use the upper end of this turbo?". If you don't, then probably a waste of time... the extra lag without being able to get the treats is pointless. If you can use pretty much all it has to give, may as well.

So I have very little experience with restrictors so like always, just sharing my thoughts. The only car I have tuned with a restrictor was years ago, and had a standard Mitsi TD05 in it and the owner was on a tight budget so the approach I took with tuning the whole thing was "to finish first you must first finish" and kept the boost curve "within" where the turbo seemed to be working safe... enough. So before I get into the strategy I'd consider doing with such a thing ( @Full-Race Geoff / @GTSBoy / @discopotato03/ usualy suspects - I am not 100% confident on this stuff so welcoming input or corrections here) is the way I understand things a compressor map is a CORRECTED airflow chart. It assumes ambient temperature and pressure at the compressor inlet is "standard" near sea level, mild day kind of stuff. As you get closer to the max flow of an orifice the down stream pressure drops, which means the "actual" air density upstream of the compressor is miles off standard and I think that if I'm right there then it's very important to not overlook the effects of this, especially if you aren't logging turbine speed etc. If you are running say 5psi BELOW ambient pressure at the compressor inlet then the air density will be much lower than what the compressor map states and the *actual* airmass moved will not be what you see on the compressor map. You may need to exist at a point >50lb/min "corrected" flow in order to achieve ~36lb/min *actual* mass flow. I'd think of it that a compressor map really is a volumetric flow map that as an afterthought is converted to mass flow assuming that your turbo is feeding on sealevel air pressure at ~20c or thereabouts. I'm not saying that going for 50-60lb/min turbo will fix this issue as the more "actual" mass flow you try and move the higher the depression after the restrictor and the whole situation will just keep getting worse, but I think it's very important to bare this in mind if you are turbo matching as well - imho if you want to map a turbo that is going to be able to achieve near 36lb/min *actual* mass flow then you should probably size it for more like 50lb/min or more if you CAN if you want to run it without overspeeding the hell out of it. Regardless of how you go about sizing it, if you are able to measure the depression after the restrictor - or wheel speed, then you can at least make smart decisions about how to do your boost curve. I would target the boost curve to stay comfortably under where it's going to start spiralling out of control as realistically when the "depression" starts really kicking into effect what will happen is the harder you push the turbo the worse the depression will get, the EASIER (weird, right?) it may become to spin the turbine faster and the sooner you're likely to explode a turbo. If the engine etc are strong enough I would 100% send it as hard and safely as possible through the middle, you get the added advantage there that mechnical loss is less at lower rpm so more power for the same mass flow. *HARD* on the engine, but if you have a narrow power curve then that's the way. I'd definitely bleed it back at the higher rpm "in anticipation" of the pre-compressor depression ramping up. If you had a way of getting a gauge on that I'd be tempted to decide what you think is acceptable and tuning it to not exceed that. Just my 2c.

I like all this. The thing that killed my ability to resist responding was the mention of modded S58s 💦 God they're good.

No worries, please don't take it as gospel - I wouldn't I don't have direct experience with this kind of thing and it just got my curiosity, though I'm sure you can decide whether stuff I've said seems nonsense or not as you look into it more. Out of interest, the Xona/FP turbos are pretty expensive but they do work to unusually high pressure ratios. I think they have got a bit more common with "restrictor classes" in various forms of motorsport for that

Yeah I've hardly ever tried doing math for this exact thing and suspect I may be going quite wrong, or maybe matchbot DOES need some work for this kind of thing. I decided to calculate the maximum airflow through a 38mm orifice with a .9 discharge coefficient (I have no idea what was reasonable so went for something big while not sounding completely impossible) and with standard ambient temp/pressure I have ended up settling on 6psi below ambient at the compressor inlet for ~31lb/min mass airflow. With this I put the -6psi line in to Matchbot using the "Default" 2litre setup, and ended up needing to run a boost curve that looks kinda like "5000rpm = 23psi, 6000rpm = 15psi, 7000rpm = 11psi" and ending up with 300hp. This results in matchbot estimate 54lb/min corrected mass flow (so what you look up in the compressor map as opposed to the actual mass flow), and a compressor pressure ratio of 4.46:1 at 5000rpm dropping back to "only" 3:1 at 7000rpm. Kinda doesn't seem toooo shocking to me, the 71mm Garrett GT series compressor is basically "topped out" at 46lb/min so it'd not be surprising at all if any amount of "gate shutting" was going to be in vain to a degree. Now matchbot DOES estimate a pretty terrible amount of EMAP for that boost, but from what you say you're not actually seeing that. Matchbot "assumes" a given amount of power needed to drive the turbine and I wonder if it's factoring in the fact that you may not actually need as much power to drive a given pressure ratio across the compressor if the intakeP is a LOT lower than ambient. Basically a lot less resistance on the compressor, kinda a trick that was used in early F1 for antilag (a pre compressor throttle that closes with the actual throttle to bump the PR and reduce drag on the blades). At this point if I were to guess, I'd say that the compressor can't even move enough air to get you to a point where the turbine is choking the engine - if I were going to be ruthless I'd try fitting a smaller a/r housing, possibly much smaller so you can bring the drive pressure enough to spin that compressor will a relatively unimpressive amount of exhaust flow. Probably a good idea to get a compressor that is more efficient at high PR as well, lol. Caveat: I'm still bloody tired and this could be nonsense, but may or may not have said something that could prove useful!?

I'm pretty fn tired right now so fair warning I may say something really stupid without realising it - but the way I read this it basically covers what I mentioned above. I might have to run into matchbot to illustrate what I'm getting at, but basically the pressure ratio across the compressor will be going through the roof and compressor efficiency potentially getting completely rooted. What will happen there is the thing has to shut the gate to keep driving the compressor but the compressor is not moving enough air to drive the turbine any harder than it already is, which is essentially what I was getting at when I said "how hard the turbine needs to work". Even though the absolute pressure in the inlet manifold is not super high, the pressure ratio across the compressor is MUCH higher than the pressure ratio across the turbine. It almost wouldn't shock me if a tighter hotside would work better, lol. I'm going to have a fiddle with matchbot now because I'm curious.

Trick is that the airflow through an orifice loosely speaking increases by square of the diameter, so a 76mm restrictor (lol) will support *quite* a lot of power. The other issue is the pressure ratio across the compressor will go up significantly as pressure drops below ambient between the restrictor and the inducer, so that starts doing funky things with compressor efficiency and also how hard the turbine needs to work... things I assume someone using Matchbot are hoping to try and anticipate.

I think it should do a reasonable effort so long as you put the right values in and the results will only suit the conditions you are applying the numbers to suit.

Not *as* suited as the EFR8374 I suggested - and only mentioned that because I thought you'd responded to my comment though OP has mentioned pump gas so gotta clarify some things as I may change that view a bit too haha. I'd prefer Sinco myself, I would look into Artec's cast divided manifold as well though there have been posts coming up suggesting that fitment may not be great so that might be worth keeping an eye on. My turbo suggestion was also assuming ethanol, you *may* need something different depending on what octane fuel you'll be running and how the dyno reads? You may need a "bigger" turbo than the EFR8374 that I mentioned if you're looking for 600hp @ wheels on say an Aussie Mainline or Dyno Dynamics rolling road dyno on say 98RON, but if you're going to be running on a hub dyno or Dynojet then it wouldn't be a problem.

Edit: Oops, I clicked the link to the thread notification thinking this was a response to my comment and said stuff explaining why I thought the G35 wasn't as suited to this situation and it could have looked like I was having a dig - and just realised you were responding to another comment. Ignore me!

Without being absolutely ridiculous about it, this is the gist of what I'd look into: - RB28 with VCam - Nismo intake manifold - If available a good T4 divided cast manifold. Smallest volume possible that is going to support 600hp, PROPER pulse convertor style thing - EFR8374 with 1.05 T4 twin scroll hotside - Good intercooler with minimal pressure drop and unrestrictive intercooler piping - Free-est possible flowing exhaust. 4" dump pipe off turbo - Run it on ethanol I'm wondering what I'm missing with people suggesting a G35 900, if there is a result or something I've not heard about I'd love to see it - from all I'm aware of so far that'd be a solid step down from an EFR8374 in terms of overall stand up/response if everything is put together and working right. Sure, capable of more power and go well for what it was but not "peers" with an EFR8374 in terms of responsiveness from anything I've seen so far. A G30 770 would be more comparable I'd have thought, and if I had seen such a setup I'd consider that as a possible viable alternative to the EFR8374 and would love to see how it would go - but I'm just suggesting unbiased and proven combos. At this point I'm not confident there is anything else that would compare that will safely hit 600hp and be as responsive.

Not to question this data at all, obviously very good input and context been given but I thought I'd add stuff from some data I've got for a car run in a hub dyno (these numbers are from a roller dyno that reads more like a Mainline/dyno dynamics roller than a Mainline hub) where we have pretty high confidence of no leaks etc. It's not for a G30 770 but should add some perspective. A mate's SR20VE with a Garrett Gen2 GTX3076R made 597hp @ hubs on E85 at 23psi at a bit of altitude, with 131,000rpm turbine speed. These don't have as efficient a compressor as the G30 770 and have the same max turbine rpm (around 145,000). Also gives a better lock on conversion of hub HP vs flow on E85 for a rwd on a Mainline prohub. If the are no leaks, the Pulsar G30 770 flows about the same as the Garrett version etc it seems like they shouldn't be at a point they are exploding at this power and I might go checking now, but I could swear others have made this power area fine already with them.

If you're not using throttle control for torque management probably not sooo much of a thing, but ignition cuts are pretty hard on stuff.... not necessarily something I'd totally expect to cause this kind of failure though. Cool yeah not familiar with the GPR so was just saying it in case it might be - and yeah with the GTR package there are ways of adjusting the boost targetting as well to avoid massive silly things from happening.

Haven't used the GPRP just something just occurred to me if you're using a package which supports torque management - I tuned an R35 using the M1 GTR package and one of the things that quickly got my heckles up was seeing the throttle pressure ratio data when trying to manage torque etc. Some competition level (Emtron as well) engine management systems that do stuff like this to ensure that you can control power delivery carefully but also have the turbo speed maintained so that when you want the torque "back again" without waiting for the turbo to respool can actually put a massive amount of load on the turbo if you're using e-throttle as part of the torque management. Like, huge pressure ratios and turbine speed - I'm not saying this is a thing with yours but its a thing that just popped into my head when @Komdotkom , mentioned "nifty stuff". If you are using e-throttle and torque management it's very much a thing to bare in mind, the conventional turbo matching stuff goes straight out the window when you start doing stuff like that as the transient situations can potentially end up operating the turbo in really strange places. Strictly speaking that can even be a thing if you go half throttle with a conventional throttle where the turbo is still targetting "full boost" and the boost control setup is able to maintain close to target, the turbo has to try and make up for the pressure ratio across the throttle as well and can end up working super hard - this is actually another reason why it can be sensible to reduce boost targets at part throttle. A small hint of this phenom is where some cars can go into surge conditions at part throttle. Pressure ratios vs flow get super odd.