Lithium

Thanks for updating with the findings! It's not over till the fat lady sings, but this sounds like a pretty likely cause of the almost contradictory symptoms in terms of typical boost control. Fingers crossed that this nicely rounds it out

Some good discussion in here, for the most part I can't really add too much to it - thought I'd add some notes to the datalog screen shot that probably aren't news to anyone but a good prop... this is assuming 25psi-ish should be the boost ceiling given the first post refers to 23psi. To state the obvious, this issue seems super weird. Turbo speed seems pretty lethagic to build, like the turbo isn't getting as much drive as it needs - and it doesn't help that wgdc keeps rising AFTER boost target then completely shuts duty at a point, which in theory should have the straight gate dump heaps past the turbo and funnily enough causes the huge drop off. It seems like pretty blunt boost control tuning but I'd not call that the primary issue, so much as possibly not helping the situation. I'm curious, what does a pull look like with purely mechanical boost control? Like purely wastegate? There are things in this log and story that make it sound like there could be a significant restriction in the intercooler piping or something - but then it's also overshooting boost target which is NOT what you'd expect with a restriction. I can see where people are coming from with the non-linear wastegate bypass (not that any valves are linear for this kind of thing), but it still doesn't make sense that it can't hold <20psi on a 12psi spring. Have you, or can you try measuring pressure pre-intercooler? Be pretty interesting to see what's happening there vs in the intake manifold - sorry if I've repeated old ground, I've kinda skimmed over but I could have missed something. In terms of comments regarding the wg spring being closer to boost target, I haven't used a straight gate but part of the reason for having close to wg target is about fighting backpressure as well - I might be wrong, but I'd have thought that part of the point of using a butterfly valve like the straight gate does you actually don't have to resist pressure at all, on EITHER side of the gate. It shouldn't need too much leverage to start opening, the spring being more to do with where it triggers opening as opposed to resisting boost & EMAP, though smarter people can correct me if I'm wrong there.

Sorry had a bit of a week and haven't had heaps of time to follow this, so apologies if I've missed something - any chance of showing a log with the rpm, turbo speed, MAP, and wgdc all in one view? Definitely an "interesting" problem, and while it's definitely worth noting that there was a similar issue with the twins I'd not completely put all bets on the root cause being the same thing. Keep an open mind, follow the data.

What transmission are you running? It's a bit tricky with the scaling, but at face value the power "curve" looks more like a "line" which is a bit odd... basically a lot more like a dyno plot I'd expect with a highish (compared to a factory auto) stall torque converter type setup. If this is running an auto then this kind of boost control challenge is definitely a thing, the rpm scale on the dyno doesn't reflect what the engine is actually doing (unless the dyno has access to the engine's ACTUAL speed electronically) and what you'll get is a big rpm flare up as the engine torque launches past the converter pump's ability to resist torque at that rpm, then as the converter starts picking up rpm it will kinda even out again and the engine rpm will pick up more steadily. The trick with this "flare up" is if it's kinda near the boost threshold for the turbo then the engine's airflow requirements to maintain the previous boost level will outrun the turbo's ability to supply that boost - so you end up with a natural flattening off, if not dip when that happens. If you are running closed loop, or even tune the "feed forward" wastegate duty cycle to deal with that rpm spike then when the engine starts settling to a more typical climb you'll actually have a situation where the gate is "too closed" and boost will run away for a bit, then have to pull down again. It's not trivial to get this perfect as most boost control systems are generally expecting more predictable engine rpm rates of change, but if you *know* that's whats going on then you can at least "accept your fate" and realise getting that area perfect is kinda chasing your tail a bit, and assume that if the rest is working sensibly and the spike/dip isn't completely uncontrolled then you should be good. Sorry if I've gone off on a tangent, but the dyno plot and boost control behaviour look a LOT like what I've seen tuning autos in the past. What ECU are you running? Could possibly be convinced into looking at logs if I get too bored this weekend haha.

I used "different strokes for different folks" quite pointedly as honestly, there is no wrong when it comes to choosing what you like. I always day dreamed about flappy paddles with fast shifts in a sporty RWD Turbo and to me the sound and feel of it cutting through gears in a steady stream is exciting, engaging, and keeps the car better balanced - I *also* like h-patterns, but I find them more engaging and fun in a nice hoonable peaky NA thing. Type-R Integra/old school NA rotary, things that are raw and need all the rpm where picking the gear and getting it sky high is part of the engagement of the whole thing despite the fact that they probably need closer ratios and faster shifts even more than a 3l turbo thing haha

What do you mean? In between the two I shared? They're the same boost This will be insane. A mate has a GTSt with a 9:1 RB30/25 with Tomei 256 cams and a Borg S362SX-E that is already a beast from the basement but has a stock 5 speed and will probably get a ZF8 one day. After the G35 900 RB26 setup I'd be lying if the topic of "Wtf would a divided G35 be like on this thing?" idea hadn't come up - you'd definitely want a wide boost control range setup with it, as even with the less responsive and potent S361 we're having to ramp boost in from very low levels in the early gears.

Different folks for different folks I guess - for me, the 6MT > ZF8 claim is wild. If I had a manual Skyline I'd be saving up fix that with a ZF8. I went for a M135i, has the N55 which resolves a lot of the issues the N54 has, it already has the ZF8, is barely heavier than an R34 GTt, full boost before 2000rpm while also being real-word-faster than my old 280kw @ hubs R33 GTS25t and doing absolutely everything better. There's nothing I'd change on it to be more like my old Skyline, tbh... it doesn't sound the same but it's got it's own awesome sound - definitely not worse. To be fair I can't argue with most of those points. I guess i was pointing it out as a comparison for a Skyline GTR and it's much closer all around there, like the weight difference between an M240i and an R34 GT-R isn't that much etc. As above, I ended up getting an M135i which is in the 1400kg range - the M140 and M240is that you can get up till 2018 are B58, ZF8, RWD and in the 1400kg range which is a bit of fun... but doesn't fit the tyre etc of the Supra. They are a run drive, though- maybe no an A90 Supra but a huge upgrade over a Skyline "sporty chassis" wise.

Mechanically that's essentially what the M240i is, it's just not pretending it's not a BMW

Almost midnight purple, too For ages I was like, dammit - GTRs are too out of my price range to start with before modding... then it turns out you can have a 3litre, a ZF8, a single turbo - all things I'd likely do (at least similar) to a GT-R, but there from factory as well as all the other nice modern car things you get. Then you look at what you can do with B58s and ZF8s, people are in the 7s with this platform already with the cast alloy block and still 8 speed.

M240i xDrive is the way. 3litre straight 6 coupe w/single turbo, ZF8, Rear biased 4WD. It's more Skyline GT-R than the R35 by miles.

Oof. One of my mates has an R34 GT-R that he initially was a "I want to go twins for response and convenience" on his stock 2.6 with Kelford 272 cams, but his friends are pests and were always in his ear about their place being in the bin. Eventually one of the 2860-5s decided to add it's own input and force his hand, so he conceded and went for a Pulsar 6262G ("G35 900") with T4 0.85 hotside. Here's an overlay of the results, same cams, same stock bottom end, same boost, same fuel, just from a pretty tidy 2860-5 install to a Pulsar turbo on a 6boost maniifold on BP98. Worth mentioning here, it may seem like a dead horse thing but the dyno plot doesn't tell the story of how much better it is to drive - transient response has completely changed the car, he used to have flat foot shifting to stop it having to wind up again on gear changes even at >7000rpm... now it builds boost faster than that even short shifting. It's 100% transformed the car before you even consider how much better it holds on: Pulsar and Garrett aren't the same, but from our experience if you're just looking for a better drive and the ability to make the same or more power I think the divided G30 770 would probably be the smallest I'd go to.

Updated with Turbosmart 7275

Looks good, will do it this weekend

I have the 7170 there, sorry if I'm a little paranoid but I'm not into clicking ambiguous links - can you share an image of it?

Yeah, Turbosmart e-gate seems the way if you really want to get fancy - though much can be achieved with a couple of 3-ports and a decent enough ECU as well.

Depends on the year/model - mine is the version of the N55 which came with an e-gate however the "PWG" (pneumatic wastegate) versions actually can also do this. They use a vacuum setup to "pull the gate open" against the spring instead of "push it open" like conventional wg setups. This naturally means they can actually control boost down to a very low level/just open the gate if they want to.

Ahh yeah, probably not too surprising - nice catch anyway, aside from being a bit of a pain. I think we've done a bit of wrestling and grinding to make sure all is aligned and clearanced nicely if it seems like a potential ongoing problem.

Ahh one of my favourite things Have experienced that with a couple of aftermarket IWG turbo setups, a hint is (usually?) the exhaust gets a bit rowdier/tinnier under normal driving around as you've effectively lost a muffler you usually have operating when you're lurking around off boost. When I do road trips in my BMW I often (don't tell anyone I do this...) run it in Eco-Pro mode which turns out to open the wastegate at cruise to keep it working as an NA and maybe a little less pumping loss by having the exhaust have an easier path, never noticed that this is what was happening until I upgraded my dump pipe and starting thinking "Why is my car sounding a bit like it's got an exhaust leak now?" - only to find it go away when I run it in any other mode. Time to go external gate

Yeah very fair, and still relatively untested on RBs - though initial results from the RB30 ECR33 in Brisbane look pretty impressive. G40 looks like it should be a pretty solid choice, a few people have used them too.

On the compressor side it looks like the best, if your head setup will support doing 100-110lb/min at 30psi-ish boost. The G45-1350 compressor looks ideally better if you need closer to 40psi for it, given both the G40 1150 and G42 1200 look like they'll be around the 100lb/min mark at 35psi and dropping from there. Bear in mind the turbine sides are all different between those three turbos, so that COULD be an influencing factor for how they all perform in the real world as well. Not sure if you've made a conscious decision to only look at Garrett or not, but at least on paper the XRE7169S matches or beats those other three at everything from 30psi up and just going from wheel size alone likely to be at least as responsive as the G40 1150 and seem to behave closer to G42s in terms of turbine flow.

Haha. I wouldn't say I am either but I've definitely been around it plenty. I'm guessing you know the dial in is basically to make a handicap to level the playing field between racers. The car with the slower dial in goes first and in theory if they run their dial in time and the faster car also does then they cross the finish time if they also have exactly the same reaction time - if you go faster than the dial in them you lose, but if you are too slow there's a good chance the other person will get to the finish line first. I'm normally supporting other cars but they were all pretty dialled and were egging me on to race as well, here's one of the cars I tune (Starlet) which ran within like 1 hundredth of its dial in through the competition: https://www.youtube.com/watch?v=inEBu-d9Gn4&t=69s

Traction wasn't bad, l couldn't give it everything off the line but was able to go WOT about half a second after rolling - good for NZ drag strips. Like one run I did a 1.96 60ft and pretty sure I was on for a 12.4 but lifted early as I was on a 12.5 dial in, and still won haha

Took the dirty BMW to an actual drag meet so I could do a legit full pass on a sticky enough track and had a quiet goal to try and beat my PB in the old R33 GTS25t The time to beat: R33 on stock RB25, Internal gate GT3076R on stock manifold tuned to about 17psi on BP98 and running on drag tyres: F20 M135i with intake, dump pipe and MHD OTS Stage 1 tune on street tyres - didn't even drop the tyre pressure: Kinda similar, and kinda way different

A lot of what you said there are fair observations and part of why I made that list, to make some of these things (like no advantage between the GSeries and GSeries II at PR2.4 in a lot of cases) however I'm not fully convinced by other comments. One thing to bare in mind is that compressor flow maps are talking about MASS flow, in terms of the compressor side you shouldn't end up running more or less airflow vs another compressor map for the same advertised flow if all external environmental conditions are equivalent if the compressor efficiency is lower as that advertised mass flow takes that into consideration. Once the intercooler becomes involved the in-plenum air temperature shouldn't be that different, either... the main thing that is likely to affect the end power is the final exhaust manifold pressure - which *WILL* go up when you run out of compressor efficiency when you run off the map earlier on the original G-Series versus G-Series II as you need to keep the gate shut to achieve similar airflow. Also, how do you figure response based off surge line? I've seen people claim that as an absolute fact before but am pretty sure I've seen compressors with worse surge lines actually "stand up" faster (and ironically be more likely to surge), I'm not super convinced - it's really a thing we won't easily be able to determine until people start using them. There are some things on the maps that actually make me wonder if there is a chance that they may respond no worse... if not BETTER?! which brings me to your next point... Why G2 have lower max rpm? Really good question and I've been wondering about this too. The maximum speed *AND* the compressor maps both look like what I'd normally expect if Garrett had extended the exducers out, but they claim the same inducer and exducer size for the whole range. If you compare the speed lines between any G and G2 version the G2 speed lines support higher flow for the same compressor speed, kinda giving a pretty clear "better at pumping more air for the same speed" impression. Presumably the exducer includes any extended tip design instead of just the backplate, but nonetheless I'd love to see good pics/measurements of the G2 compressors as everything kinda points to something different about the exducer - specifically that it must be further out from the centerline, which means a lower rpm for the same max tip speed and often also results in higher pressure ratio efficiency, narrower maps, and often actually can result in better spool vs a smaller exducer for the same inducer size... no doubt partly due to the above phenomenon of needing less turbine speed to achieve the same airflow when using a smaller trim. Not sure if this is just camera angle or what, but this kinda looks interesting on the G35 990 compressor tips: Very interested to see what happens when people start testing these, and if we start getting more details about what's different.

No worries. They have a section on their website with some RR options listed, no doubt you can find out more by EMailing as well tho Reverse Rotation Motorsport Turbochargers – Xona Rotor