Lithium

I'd say closer to OG GTX3582R, just smaller trim - so 59mm inducer/82mm exducer as opposed to 62/82 for the first gen GTX3582R. Yeah EFRs were boss, the EFR8474 is still an absolute beast and it perplexes me that people still go to things like Turbosmart/Garrett etc when the results people are getting with those are pretty unremarkable compared to what you could get with a turbo available well before those options came out. DriftSquid (I think) "upgraded" from an EFR9174 to a Turbosmart turbo and promised a comparison video - and kinda shuffled awkwardly and did a bit of diversion from the fact that they didn't get any improvement going to the currently massively hyped brand of turbo from a turbo that was a bit of a frankenstein that had been well superceded in it's own range before the Turbosmart unit he put on there even came out. I suspect the EFR would outperform most Xonas for what a lot of less-insane RB owners would go for, in the 400-600kw range but the Xonas are looking hard to beat up to maybe in the mid 700kw range at this stage- basically where EFRs don't really reach, and before the Precision turbos take over. What the Xonas do well in the "EFR range" is be easier to package etc, and work very well if a divided housing doesn't suit your application.

Yeeeppp, been following a lot of the testing on the latest Xona stuff and there are some mental results. He also went over 1000hp @ 4 hubs on his Mainline with a XRE6364S (63mm) which was also well into the 20psi range before 4000rpm on a 2.5. Crazy stuff. Fwiw the XRE5964S is basically the modern equivalent of their old HTA3582 - would drive nicely enough on an RB25 or 26, but proven capable of a huge amount of power if you want to spicy with rpm tho even at sane boost levels will make stout numbers

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