Lithium

To be fair passengers who aren't silly and have been in proper fast cars have often been pretty impressed once you hit 4th gear

Outstanding!

The S2 R33 and R34 both run a nylon composite compressor on a ceramic turbine. R34 has a larger a/r turbine housing

Good luck!

Whoa, that's a name I've not see for a long time! Sorry to hear about the engine / turbo damage. Fwiw with any engine problems it often really a case of just seeing what happens when it's apart, ymmv - I wouldn't rule out the possibility that the damage isn't even from the turbo failure, or possibly from a combination. The airflow between cylinders isn't dead even, injectors can go off over time as well, with the turbos overboosting if you didn't have upgraded fuel system there could have possibly been a bit of leaning out - stock triggering is often a bit unreliable by this age too. Basically its an old engine and a few things could have been going on, and you won't know how much work is needed until the engine is apart.

I feel like this is due an update

This is a story of my life things, I learned eventually (thanks to someone calling me out) that my enthusiasm for discussing and sharing ideas that it came across as arrogance and I'm like... WTF?! One thing I'm pretty sure I justifiably pride myself on is knowing that everyone will have things they can teach you, and you're always going to find out that something you think you know turns out wrong - you just don't know what it is until you get there. Just the bursting enthusiasm that comes with ADHD when you hit something that gives you dopamine dumps can come across like you think everyone else is wrong or don't matter. But yeah, I'm a software engineer by trade and also do tuning in weekends and 100% have long had a reputation for quickly making connections when resolving problems or forming solutions that I've sometimes had to take people form a long walk from start to end to explain how I ended up where I did when it's seemed "too simple" when I've stated my initial case, and had the "WTF" type reaction when they've realised how much was actually considered haha. My reward is that I get all the curly problems thrown at me.

Cheers, and cheers for sharing so much of the build and also sharing the glimpse of what turns out to bring a lot of us poor decision makers together haha. I do recommend learning more about how to manage it, if not considering getting a formal diagnosis. The discussion with the psychiatrist I got my diagnosis through was quite eye opening, things I'd not even considered to be ADHD related and hadn't mentioned were things she asked about out of the blue and were common themes with people with my flavour of ADHD. It's not a label for people who are hyperactive and ill-attentive, there's more to it than that and some of it can be much more challenging or damaging - though there are of course two sides to the thing, and a lot of the stuff we have to go through and work on to live with it make us effectively "better" at other things as well. Aside from the fact that there is some argument I could have a bit of ASD seasoning in there (came up during the diagnosis, and neurodiverse things seem to not stay as a cookie cut) I suspect you need to learn more about ADHD if you are puzzled about how hyperfocus could possibly apply. I *do* personally use "superpower" with quotes deliberately, but it's 100% an ADHD thing due to the exact reason that lack of focus is also an ADHD thing... Loosely speaking the inattentive side of ADHD isn't the inability to focus, it's the inability to control where the focus goes. Not being able to sleep because brain is more interested in thinking about a stupid thing I said to a girl I liked 30 years ago, not being able to focus on work because my brain is more keen on putting together the torque management strategy we're going to try out with a drag car next weekend, not being able to focus on a conversation with someone I WANT to listen to and respect because there is a flickering light in my peripheral vision. If I could just stop work and build the torque management setup right there and then I'd not hear anything else until it was done.

I've been quietly following this thread for ages, but this one got me. Since my ADHD diagnosis (and associated learnings and prescription) I'm way less inclined to wade into forum yarns when there are better things to do with my time, as half the time I'd end up in some kind of forum debate even if that wasn't my intention. I've not lost the ADHD "superpowers", just am a lot better at directing my hyperfocus into slightly more constructive things, but haven't stopped quietly lurking in here in my spare time.

Right. I'll try my best at a concise "bring you up to speed" on stuff that may be missing here - obviously open to questions or further input from others as relevant. Here's a datalog from a responsive turbo setup with electronic boost control being used a bit, to keep it simple I've marked 3 points of interest. All of these charts are on the same time scale on the X-axis, so you can reference what engine rpm is doing in the top graph, boost and EMAP (exhaust backpressure) in the second graph, and turbo rpm in the bottom graph. A) The turbo gets it's power from exhaust gas, and pumping air takes work. As a result you can't just spin a turbo with a fixed amount of exhaust energy and expect it to keep spooling - the bigger the turbo (ie, the more air it can push) the more exhaust energy you need to drive it. The most obvious ways of getting more exhaust energy are by adding displacement, adding boost, or adding rpm - but as you add any of these the turbo also needs to do a bit more work so there is a big balance of these things needed to even get to your target boost and sometimes that's not even possible. What you can see in step "A" is that there isn't enough engine rpm or boost to reach the level we want, so this is where "lag" is. The dyno run continues and rpm increases, which gives enough energy to increase boost, which helps spool the turbine speed up even more - so you can see that the rate that the boost (and turbo speed) are starting to ramp up faster than the engine rpm is, so turbo is really starting to wake up as the graph gets closer to point B.... B) At this point we've been able to reach the boost that is actually desired at this point. To stop the boost from going further than this the wastegate will open and bypass gas past the turbine, meaning it doesn't continue accelerating at the point it was before but instead carry on at a more progressive rate which matches what the engine needs. The wastegate will have a spring in it which is rated to a specific pressure where it will start bypassing, but electronic boost control (managed by the ECU) can adjust how much pressure the spring sees in order to allow some tunability on how much boost the wastegate actually sees, and therefore how much exhaust it bypasses. The tune in this case stops boost from ramping up HARD at around 21-22psi just before 4000rpm, then as the rpm continue it allows boost to continue up to around 25psi higher in the rpm. You can see the turbo speed fairly steadily increases through the rpm to ensure it's keeping up with the increasing airflow demand due to the engine speed being higher and boost being pretty steady. If the boost dropped off after a point then you may see the turbo speed level off or even drop. C) You can see that despite the boost pressure staying pretty flat here, the exhaust pressure is steadily increasing and at this stage has overtaken boost pressure. This isn't unusual, and is largely as a result of the increasing energy needed by the turbo to pump more and more air to suit the needs of the engine as it revs out further. There are a bunch of variables in regards to how much back pressure there will be on a given turbo etc, but its one of the factors we manage when sizing and tuning a turbo setup. When exhaust back pressure starts exceeding boost pressure you will eventually start seeing signs that the turbo is running out, the engine gets less keen to make more power and it gets harder to raise boost further. In this case it's a fairly acceptable compromise for the power level (around 630kw on a 3litre engine with full boost by 4000rpm), but you'd not want to push it a lot harder than this. The maximum speed rated for the compressor wheel on this setup is around 125,000rpm so you can see its starting to get close on that side as well - I feel like this kind of illustrates some of the turbo related things we both decide on how far to push, and are also limited to how far we can push depending on the parts combination. Hope this helps more than it confuses things

I was actually going to try and dig out a datalog with turbine speed and EMAP haha

As someone who has been playing with turbo things for some time now, be prepared for this to not be the first time feeling this way I'm busy as atm, but if no one else covers the things I'm realising are worth mentioning to you then I will when I have a chance as it seems like I overestimated your knowledge on how turbos and wastegates work. Otherwise I recommend having a look around how wastegates and boost control work, really anything on understanding the general mechanism of boost control as it will help you find the answers to the questions you're looking for. Your initial question jumps some fundamentals.

Good points! Took those for granted - though I *did* actually give an example of winding boost up more than it had been before where I wasn't actually specifically looking for more peak power. The Toyota Starlet dyno plot that I shared and mentioned showed an overlay from the previous tune it had and the one I'd redone, I left the boost targetting the same as the old tune but then after peak power I ramped boost up by a good 5psi or so over what the old tune had at the same rpm. The reason I felt comfortable with this (though the owner of the car had a "are you sure?" moment when I suggested it) is that the setup wasn't turbo limited, it was largely head sealing limited and the owner was a bit concerned as for the last few seasons he'd had issues with head lifting - sometimes not completing an event without having some headgasket issue, so he didn't want to run any more boost than it was. The reasons I was ok with raising the boost a good 5+psi MORE than that was that I left it where it was in the middle, and only increased it where VE (and therefore cylinder pressure vs psi) were dropping hard and I didn't stop the torque from dropping, just reduced the drop. Well, there is that and the fact that the previous tuner had it overtimed by near 7degrees at peak torque - but that's another story haha. I didn't really go into detail about that "turning it up more" thing but now you've mentioned the "not detuning", sometimes the boost *can* be turned up higher than you'd expect if the setup allows for it and you do it smartly. I've tuned things to run 30psi on BP98 "safely" that a few years ago (or still?) people would cry that it was a stupid idea - but given they were well intercooled, low EMAP turbos and only doing that kind of boost where VE is dropping etc I was pretty confident it wasn't as cowboy as it sounded at face value and we never ended up with issues as a result of it.

There is a LOT of stuff that can be done, it all depends on how much time and money you want to spend on doing in. Not all ECUs will be able to do it, and the more control you need the more time and knowledge needs to be put into making it work. If you're willing to spend the time and money and have the right hardware and skills involved there's a lot that can be done.

Correct. In the case of the 500kw dyno plot I showed you the car actually runs two boost control solenoids for boost control and a 5psi wastegate spring. It allows me to control how much boost pressure is applied to both sides of the wastegate valve at any point and fairly accurately control boost target as a result. I've tuned it so that it's able to target anywhere from 5psi to 25psi depending on what's needed. The target tables I've set up in that car are Gear vs RPM, so every gear has potential for a different boost (and torque) curve. First and second gear have quite low boost targets, third gear actually has different target boost all the way through the rpm range as it's a stock RB25 gearbox - the boost targets have been chosen to maintain a peak of 600nm (what the owner has set as the maximum torque he's happy with putting through the stock 3rd gear) but it carries that to the rev limiter. The boost curve to achieve that is something of a ramp up, then hold, then ramp up again and the power curve looks more like a flat line haha.