Lithium

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.

That's torque and power, it's all from a single run. The boost curve is "held back" from it's peak target in the 3500rpm to 5000rpm range from memory, so it ramps hard to something like 18psi then climbs more progressively to 23psi nearer 5000rpm. It makes the torque (and power) ramp more "natural" and less hard on parts and traction, it doesn't feel artificially held back.

Here's the torque curves from the car I ramped boost up later in the rpm to allow a slightly wider useful power curve - the power curve is a bit weird shaped also thanks to the TVIS (or whatever they call it with the 4EFTE in this Starlet) which changes the volume of the intake manifold throughout the rpm range, but you can see that the green power curve actually holds later on with the extra boost... but looks almost more like the kind of thing you'd expect from a cam or exhaust change

There are a few variables here, some are relevant but not critical (IMHO) to help answer your question. The two major things: 1) Ignoring anything to do with forced induction - all engines have their own natural torque curve, and it will ALWAYS roll over higher in the rpm. There is a fixed relationship between power and torque. When dealing with kw and nm, the relationship between them is roughly: kw = (rpm * nm) / 9549 nm = (kw / rpm) * 9549 The peak torque of an engine (without boost) will typically climb until somewhere nearish the middle of it's operating rev range, give or take a bit - then start dropping again. The nearer the minimum and maximum rpm of the engine the steeper that drop off tends to be. 2) Boost simply increases the density of the air going into the engine, which inflates the torque at that point. The ramp up in the torque curve you see on a turbo engine is due to the boost rising, but it's essentially just multiplying the torque you'd see if it was naturally aspirated. The roll over you see at the end will typically be what would have always happened with the engine, whether it was naturally aspirated or turbocharged. If the torque never started dropping then power would climb infinitely. The cool thing about this is you absolutely can tune the power delivery to suit the needs of the owner and/or the limitations of the car, and I regularly do this. With modern turbos we've got to the point where a setup that someone may run well over 20psi of boost with could actually reach target boost well under 4000rpm if the tuner/owner WANTED to - and a lot of people seem to do this when there is actually no realistic benefit, generally it just adds a massive amount of strain to the engine and drivetrain and often actually makes the car harder to drive. As a general rule I tend to tune the boost curves for cars I tune to reach a "useful" torque level through the rev range and will often end up with a curve that ramps hard to a point, then creeps for the rest of the rev range - not to make the boost curve "soft" as such, but more to make sure its neither laggy nor pointlessly violent in it's delivery. There have been cars I've tuned to be almost like a centrifugal supercharger (or naturally-aspirated-ish) where they actually only hit like 8psi of boost before opening the gate, then ramp up the next 10psi over the rev range... if the car is "loose enough" to drive. On the flip side I've tuned a car that had stock cams and the engine's natural torque curve fell over HARD in the higher rpm and resulted in a slightly awkward power curve to work with, in that case I actually started ramping up boost to boost torque in a way to offset the engines "NA" torque drop off... at peak rpm actually running a good 5psi+ more boost that what the "flat curve" would have defined. This gave the owner an extra 500rpm or so of useable rev range, and had a fairly solid impact on times he was running at motorsport events due to being able to hold gears a bit longer and also falling into a more useful part of the rev range in the following gears. Here's an example of an RB in a GTSt I've done the "softened" boost curve to not pointlessly ramp straight to the max boost target early in the rpm, but still made sure it builds useful boost. If you went in the car you'd not guess at all that the boost curve was doing anything "weird", it feels like it spools immediately and accelerates relentlessly (traction dependent) and holds to max rpm. I don't know if you'd guess what the boost curve was doing by driving the car, or even looking at the dyno plot... but imho it suits the combination.

The GX-R turbos are mostly more about classes than outright response vs power, which is why there are 64, 67/68 and 73mm versions. They are an improvement over the existing inducer options at least flow wise but given they're G42 and G45 turbine options they will be a LOT laggier than the EFR9180. 109krpm isn't tip speed, thats rpm - the reason the rpm is lower than the likes of the 9180 is because the tips are further from the centre, meaning tip speed will probably be HIGHER than the EFR9180 at it's max suggested speed. If I had something like your car and the things you sound like you're into I'd probably be most interested with the Xona Rotor XRE7169S, it'll have a response hit on the EFR9180 but you won't get a more responsive turbo than it that's capable of >1000hp.

My opinion is they aren't worth double at all. Have used a good number of Pulsars with builds I've been involved with and tbh at least speaking for myself, Garrett aren't losing money they'd be getting if Pulsar didn't exist as for genuine Garrett money I'd probably be buying something other than Garrett. We've used Pulsar 6262G (G35 900 equivalent) on an RB26 with a twin scroll hotside and it picked up 40wkw at the same boost over the old twin -5s and the improvement in transient response over the twins changed the car - this is before you factor in the amount of further headroom of the G35. Have also used one on a 2JZ drag car which has run 9.6 @ 141mph not even trying, from what we've seen so far it'll potentially go 8s when we turn it up Crazy results for what is basically a NZ$1500ish turbo.

I've never seen Garrett say not to worry about twin scroll - they have twin scroll options for all their G and GT series turbines from the 30 series up. What kind of dyno are you expecting to be making 500whp on? So far it sounds more or less like you're doing a G30-770 kind of setup, and realistically an open housing will be good response etc

A group of friends hired the local drag strip off season, cold weather and no prep means it was super slippery but still allowed for a fun day of 1/8th mile (no ambo meant we couldn't do side by side 1/4) roll racing and Dragy runs. The wee BMW didn't embarrass itself at all considering the 2WD group I was competing in had a couple of supercharged V8s (an LSA and a blown LS2), a 600kw M135i, a 500kw R32 GTS-t and some other spicy things - I actually ended up beating the blown LS2 & 600kw M135i heads up in roll races and faced the GTS-t in the final, losing by just over a carlength which is far more than I was counting on with a very mildly tinkered with M135i. For transparency sake this was EVERYTHING to do with being a fairly short distance on a shit track and having something without any lag and a brilliant gearbox, on a prepped track or a full 1/4 I'd have been destroyed. I did do a single sneaky full (well actually turns out I hit the brakes 10 or so metres early) 1/4 mile Dragy run and hit 12.88 @ 109mph on the brakes which is precariously close to my PB in my old GT30R GTS25t that ran 12.6 @ 111mph on Hoosiers Pretty damn stoked with that considering I had a single attempt, and despite seeming well suited to the conditions vs the higher power cars and the time slip not looking THAT bad I still was having to work hard to not just do a rolling burnout <100kph and doesn't really show it's best at all. I am pretty sure it would happily match the old R33 with a full run on a better surface

I've never had a T51R mod done on a turbo but can answer things to at least give you things to consider. Firstly, I'm pretty sure "T51R mod" is not going to be a completely standard identical design. Different folks will make their own calls on how they want to make the sound, and different compressors and housings will give different amounts of space to work with as well - so the design and effect from company to company and turbo to turbo will be arbitrary. In terms of "is it the same", no... it won't be, I'm pretty confident of that. Whether it will have a negative (or NOT negative for that matter) effect really would be foolish of any of us to speculate on without any data. Surge slots, or map width enchancement grooves basically bleed air from part way up the compressor out to the compressor inlet... effectively from the turbo's point of view it is an air leak that allows the turbo to be re-fed with the air that has been leaked. When done "right" it can allow air that the turbo can't pump into the engine efficiently to spill back into the intake as opposed to cause a surge condition. Simply put, it has a direct effect on the efficiency of the compressor wheel. When you are getting up to the maximum capacity of the compressor wheel the design of the intake and compressor rely on every bit of area of the inducer etc to work as efficiently as possible, if you have something literally designed to cause a leak of turbulent air (to make the sound) back to the intake it's hard to imagine there won't be some cost to the higher end of the flow capacity but I wouldn't dare even try and guess if it were either major, or academic. Just bare in mind there will be an effect. On the "upside", I'm assuming you are going to be running the 1.05a/r hotside you had on the EFR9180 as you mentioned you don't want to do any fabrication work, and the 1.45 hotside DOES need the dump pipe (and as such, possibly exhaust) shifted as it actually pushes the turbine outlet further from the CHRA... its a huge housing. I doubt you'll be able to safely push the 1.05a/r hotside on pump gas far enough for the 9280 compressor to actually start getting to the point you have to worry about sacrificing a bit of flow for sound. As you know, I'm a big EFR fan where it suits - unlike some, I just go on merits and suitability for setups and there are a lot of cases they are unbeatable. In the case of where you're going though, I'm not convinced that line is the best thing for the job. To do it right I'd either stay with what you have, as you're finding it's pretty hard to make the car more powerful than it is without sacrificing "something" - or do a "proper" upgrade to an all new beast that has the turbine flow to support what you are looking for, and arguably also has the T51R sound and vibe which I'm hardly going to throw stones at you for looking for... you'll remember that my turbo choice for my old R33 was absolutely influenced by the induction noise the GT3076Rs make haha. Given the price of an EFR9280 and T51R mod, any work to get it installed and tuned to suit may turn out to give a result that makes you wonder if it was worth the effort - but if you're willing to spend that and not worried about massive gains, I'm pretty sure what you're proposing *will* give you some of that sound and probably stretch the power out a bit further in the rpm. I've so far not heard any unmodified EFR sound "whistly" like what I'm assuming you're looking for, though.

I'd verify how invested in exactly 9.5 he is if it turns out to be a massive amount more effort to go 9.5 vs 9.0 or 10.0. He may have just said that as a suggestion not realising it'll be a huge deal to go specifically there when half a point either side isn't so bad.