Lithium

Well he's got the advantage of having had it on his dyno and seeing where the potential is so thats pretty promising, I guess if VCT isn't (but can be) enabled there's definitely gains to be had just there. Sounds quite promising, and basically means GTX3076Rs will be full boost at ~3500rpm on RB25s which is pretty sweet.

4K actually sounds around about what I would have expected for that setup, thats not too bad.

I'm real fussy and actually tune for both VCT on and off, if you just change the point without adjusting anything then you get a misleading impression of what the potential of what VCT really gives. With VCT on, the engine actually likes more timing (at least up till around 5000rpm or so) than with it off - which actually changes the curve. If you want to find the perfect point for your car, optimise the tune for both on and off then overlay the "best" for both and set the engagement and disengagement points to allow the highest torque curves to be utilised

The taller/narrower islands would probably be a result of the increase in trim, I'd have thought? And in regards to increasing the exposure of the blades to the ports, no doubt it would increase the compressor's ability to gain outright shaft speed but unfortunately the shaft speed is just one part of a puzzle which involves getting air into the engine - anyone with a boost leak can vouch for the fact that more shaft speed doesn't (necessarily) mean better response. I'm sure there is a fine balance, but my understanding is the main purpose of the ports would be to try and stretch the surge line and islands between for given pressure ratios to the left (funnily enough, given the whole anti-surge term) while maintaining a balance between that effect, spool and trying not to topple the choke point. Wouldn't exposing more start eliminating some of the advantage of the higher flowing 58trim wheel? Just trying to get an idea of exactly what you're envisaging by that, or if I am on the same page.

Hell yeah. Makes me want to see what even a normal gt 30 will do with a .82 with e85

Yeah fair enough with the stock internals thing, hours result in terms of loading no spool though. Both turbos clearly have more to give which is pretty col in its own right

Yep more boost if the engine was getting to such more air would potentially show where the gtx starts coming into its own

If the new turbo can flow more than the old one then potentially without raising the boost and/or adjusting the tune to maximize the new found goodness then potentially not really telling of the real difference. That result suggests to me the old turbo had more on it too...

Interesting result, cheers for sharing... Did you do no tuning for the change?

Sweet, good on them - good luck and let us know how it goes

Thats why god made Holset HX35s That was my preferred choice when I got my GT3076R, but I was concerned at the effort to make it work. If I could I'd go back to 2006 and tell myself to go a twin scroll HX35 on a suitable manifold/wastegate setup.

The trick with that is that you still can't see the response, when a car is lagging the earlier part happens slower - then when on boost it happens faster. Acceleration has a cumulative effect on "eating distance" so a little difference in torque earlier may have a bigger (or less) long term affect than the dyno plot may have it look like... if you have a way of working out how much affect the lag (and after the lag) has in the real world then potentially it'd build a better picture of whats actually faster. The dyno will never show how the car reacts to snapping from 10pc to 100pc throttle at 4500rpm, for sake of arguement.

I started this thread to see if people were interested in trying to nail that down instead of speculate too far. The higher the engine speed, the smaller the difference - realistically. The main things that cause lag are the overall rotational inertia (the majority of the inertia comes from the turbine wheel which is made of heavier materials) and the wheel design. Both GT3076R and GT3071R have the same turbine which is the source of most of the inertia, and they are both 56-trim GT-series Garrett compressor wheels... on the same turbine shaft etc. For the sake of picturing the effects of the differences between the two turbos in an overly simplified way - lets pretend both the compressor and turbine wheels on a GT3071R contribute evenly to inertia and try and work out how much more work is required to pump a certain amount of air. Even without counting the fact the turbine and bearing resistance contribute way more to the equation that I am giving them credit for, the increase in the moment of inertia going from a 56trim 71mm comp wheel to a 56trim 76mm comp wheel on a GT30 core could result in at tops a 7% gain for 13% more flow potential. Take into account the GT3076R pumps more air for the same rpm - ie needs ~104000rpm to push 25lb/min at 1.5bar of boost whereas a GT3071R needs ~112000rpm (9% more rpm required than something with 7% more inertia!?!) it stands to reason that in terms of transitional throttle a GT3076R might not be as bad as you'd expect. That is very overly simplified (the maths and such forth get long winded and I should be working), but thought I'd just give some crackpot theory to the comparison

Because can't see myself convincing a range of people to come to Wellington, NZ with different modified Skylines, hack the intake up to accomodate a VH45 AFM and run them on a dyno as easily as it would be to get someone to go for a quick jaunt with datalogging going I wouldn't want everyone to have the same turbo combo, that defeats the purpose. The kind of thing I'd be looking for is stuff like 2500-3500rpm in 2nd gear, 3500-4500rpm and stuff like that - and also boost curves for the same thing. Keeps it simple and more accurate than someone saying "My T3/T04S makes full boost at 3100rpm" and everyone else going and buying T3/T04Ss based on that comment.

A large percentage doesn't have to be over half, there are lots of people running Links (including the Links rebranded as Vipecs)... enough of a percentage to do something if there are enough people keen. If nothing else, if we came up with a common CSV format to abide to then we could look into making converters to extract the necessary info and output in that format.

Its not nothing obviously, but in the ranges you're likely to be utilising the power the difference in spool will be negligable... especially with a twin scroll housing, which is what this is about. By setting your power ceiling to the most a GT3071R you do artificially give a GT3071R the advantage, though it'll be such a small one it'd be hard to quantify and that kind of conjecture is totally missing the point of optimising the turbo match to an engine - it makes it seem like you're just making up rules to push your view point. Keep it separate, a car running a stock turbo would be faster than a car runing a GT3071R if they are both running 9psi - but that defeats the purpose if you have a car built to run a GT3071R to its potential.

Hi all, There are heaps of threads around on different turbo and engine combinations with these cars. There are clearly different preferences people have, and some people in their enthusiastic like or dislike for a particular combination will often smudge fact a bit. What occurs to me is that a large percentage of people on here will be running Links/ViPECs, and have similar gear ratios and cars. Who else thinks there could be merit in doing some Link data log sharing to help get an honest comparison of what happens with these cars? We could agree on a few key tests, such as full throttle from 3000rpm, 3500rpm, 4000rpm and 4500rpm in 2nd and 3rd get etc - and export the log files and find a way of sharing them around. If there is enough interest, a little project I've been doing in my spare time (in between playing cars, drinking, working, forum whoring etc thats not necessarily heaps ) has been putting together software similar to VirtualDyno for EvoScan for Links which was intended for helping me out when a dyno isn't available for doing a bit of tuning, I could try and tweak that to put together suitable comparisons... I'm sure other people are capable of "things" too. Just a thought, hair brained or has some merit?

WTF? Ok, I know you and some others have seem some grudge against GT3076Rs but seriously - that post is just being silly. You don't have to like them, but don't muddle things up by making comments which are basically saying "A car running an ever so slightly larger turbo is going to be so laggy and have so little midrange torque and so much more power that it will probably be slower". Try and stick to facts for people who don't know better. My thoughts: 1) The throttle response is going to be so tiny between those two turbos its really not going to make any difference unless you are having rolling races from 2500rpm-3500rpm, and its going to be hard to call the start accurately enough to determine if its a reaction time or a spool thing separating the cars. Once you are actually in the "fun" part of the rev range, the throttle response is going to be so small I'd venture to say it'd be impossible to quantify the difference. 2) Midrange isn't going to be higher on a GT3071R unless you are running more boost in the midrange, which is a tune thing. Both turbos will be at their controlled boost level well before "midrange" 3) Midrange punch is the most likely part of the rev range where traction will be broken - make up your mind, you want to over come the tyres or you don't? 4) Faster = sum of the parts, if a car can handle everything a GT3076R can throw at it (see Tomei STI, one of the fastest time attack cars on the globe) then its going to be faster than a GT3071R equivalent... albeit not much. If its going to be slower because of the power a GT3076R makes over a GT3071R, like the response - there isn't a night and day difference between the GT3071R and 76R power potential, you're probably already having the same issues with the GT3071R. This has given me an idea....

A twin scroll GT3071R on an RB25 would be pretty mental - I'd personally make the most of the extra transient response and torque boost the twin scroll gives and use a GT3076R, forgot all the ideas you have about the different turbos with the single entry housings and don't get too hung up on boost curves only having a couple hundred rpm difference in spool... the big draw to twin scroll to me is the increase in VE, remember we run more boost to boost torque but thats not the only way to do it. Here is an overlay of an SR20 going from a .64a/r GT2871R to a twin scroll GT3071R from Full-Race: I really think a twin scroll GT3076R would be the ideal on an RB25DET, we already know GT3076Rs are barely noticeably laggier than a 71R and with the extra boost in transient response and inherant torque gained with twin scroll - basically a twin scroll GT3076R should out grunt any open housing turbo bigger than a GTRS... at least once it has over 3000rpm on it. Food for thought?

Whatever you want to put up Boost curve and power are probably the main ones... thanks!

That result sounds a bit more like it, are you going to post a dyno plot?

Wasn't sarcasm at all - see here: http://www.typology.net/quotes/maria.html Forums are full of people who think they know more than they do and sitting on people who may actually be heading in a good direction, even if in a round-about way.

Good on you for striving to do your own research/experimentation to satisfy yourself that you've done it right - there IS a lot of BS and misunderstanding on the internet and its self propegating, I wish I worked out way earlier that even a lot of the more clued up seeming (and sometimes actually are mostly switched on) people have holes in their understanding of things, no one can have all the answers. A lot of the time given explanations for a rule of thumb which is correct are wrong in terms of reasons, and thats where things can go awry. Having said that, all things being equal (no compromising bends, equivalent mufflers etc) I am absolutely sure that going to a 3" or bigger exhaust will cost you nothing anywhere versus a 2.5" system on your car. Any loss in torque anyone has experienced with a turbo car as a result of changing exhaust would more likely be tune related, or some other issue - especially if the airflow (in an airflow metered car) reaches levels which there is overly safe mapping for in that particular instance. Bare in mind when changing a cars setup that there are always all sorts of variables at play, don't always assume that the most obvious thing (or the first thing you think of) is actually the cause of the final outcome.

Yeah, seriously - 4"... do you realise how much of a mad combination you've got here? I'd probably have gone for slightly larger cams, but regardless - this thing is going to have such an insane amount of power everywhere it makes me fizz.

Nice dead thread resurrection. Given the thread name is "max hp out of standard RB25" its kindof obvious why an RB30 isn't involved. R33s come out with RB25s standard, if you want to go fast but don't want to (aren't ready to) extend to building a new motor then just doing boltons to the stocker makes things a lot more affordable - the thread is about seeing how far you can run with that. Here is a video of a mates R33 doing a 10.6 running an RB25DET with stock bottom end on BP98, no NOS etc: He didn't spend the extra money on a 30 because he wanted to see how fast he could go with what he had