Lithium

I personally wouldn't bother with a GT3071R with a .82a/r hotside, but since you're asking - I'd say you'd be pretty hard pressed to tell the difference between a .82a/r GT3071R and a .63a/r GT3076R in terms of response. I would like to know how different a GT3071R and a GT3076R with the same hotside would be, even - I am sure there will be a little difference but it can't be a huge amount! Going from a .63 to a .82a/r housing made my GT30R slightly lazier up to 3000rpm, the rest of the rev range it seems much of a muchness.

GT2835/GT3071R are more or less the same thing. On a completely stock RB25 up to around 16psi you are unlikely to see much advantage on a GT3076R vs a GT3071R as they have the same turbine flow and the GT3071R's compressor is still fairly efficient up to the mid/high 200rwkw mark. The GT3076R will start shining as boost or flow (ie, doing cams or other such mods which improve your engines efficiency) start going up. Given the spool between the GT3071R and GT3076R is barely different and there is a good 50hp more to be had from the GT3076R I found the GT3076R a better compromise given one can get greedy.

We tuned an R32 GTSt running a stock internal RB20 and a generic T3/T4 thing with a 30% blend we made up using E100 mixed with 98 running roughly the same boost as its previous pump gas tune. The reason for the E30 mix was basically for the reasons you state, partly influenced by the fact that we figured that E85 would be too much for the 444cc injectors it was running. We did a base run at 20ish psi on standard 98 and it put down 247wkw, then we drained the tank and put the "E30" mix and retuned it and ended up making 294rwkw and improving spool by a few hundred rpm. It was definitely worth doing, imho

If you can't run into the 140mph range with a GT35R, you aren't trying hard enough The 600+hp dyno plot isn't relevant to the comparison we are seeing here... a before and after with the same car and same dyno, run to the limit each turbo will make with that setup has to be the most fair comparison you can get - surely? It represents 15% more power with 19% more revs needed to reach 20psi (to rule out the boost controller differences, and make a bit easier on the T04Z). Far cry from earlier in the thread where people were implying the T04Z is comparable to a GT35R in spool! I'd love to see a GT4088R compared with these things

Its not quite that easy, but as an overly simplified view of it - yes. This kind of thing is why we have compressor maps showing percentage efficiency at different flow/pressure levels. There are cases where smaller turbos have higher compressor efficiency at equivalent flow rates - this can be but isn't strictly at the higher pressure ratios/lower flow levels and could partly answer why some smaller turbos can be perceived as torquier. Bigger compressors tend to make and hold their efficiency at higher flow rates, which is why they tend to be capable of making more power at lower boost. The turbine flow comes directly into it as well, as the easier the exhaust can leave the engine - the easier more fresh air/fuel mixture can enter the engine.

I sortof agree with the above explanations, however strictly speaking I'd say the engine is the "hose" bit of that explanation - the turbo is something different. The turbo has the capacity to pump a given amount of air at a given amount of pressure, but the engine has a natural capacity to move a certain amount of air at atmospheric pressure. Any more air than that and the engine starts providing the turbo with resistance, which is (partly) where boost comes from. Pressure also increases with heat, so if the engine is able to breathe more than a turbo can move at a given pressure - then yes, you are likely to get more power on the same boost with a bigger turbo. If the turbo is able to pump more than the engine can breathe at a given boost level however, then going to an even bigger turbo will probably not make a lot of difference...

Nice! Will be good to see how it goes, especially if you go the E85 path again. With a twin scroll T4 GT35R you'll probably lose very little response.... I'm kindof umming and ahhing about go that way

Mine has done it for a good 70,000kms so far - maybe more... I lose track. I am pretty sure I first noticed it in 2005. Since then its seen track time, god knows how many drag runs (a good number of which reasonably into the 12s) , dyno runs, street driving, compression tests (with good results), 3 different turbos, up to 20psi of boost, a new cam belt and it seems no louder than it was when I first noticed it. I have no idea what it is, but am pretty sure that if it was bearing noise or a damaged piston skirt I'd have known about it by now!

What, T04Z? Would you put it on the RB25 as it is?

I usually avoid screaming noises during spool by either not running as much boost, or not taking passengers

Depends on what you want really - I'd be more inclined to go the above using a GT3582R but for an RB25 a GT3076R with twin wastegates etc on a FullRace type manifold would be pretty fantastic. Hell I am rapt with my .82a/r T3 internally gated GT3076R on my RB25 and I'm not even tapping its flow potential yet. I couldn't imagine the same thing with better spool, less restriction and 22psi pumping through it!

I see ATPTurbo now have a 1.06a/r T4 twin scroll turbine housing for the GT3076R.... this has intrigued me quite a bit! I can't help but think that could be very interesting to try.

Not true, the dyno controls the speed the car revs out... so it doesn't really matter which gear it is in, in that respect.

GT3071Rs are .5comp cover, real GT3076Rs are .60 antisurge...

The bearings can make quite the difference with Garrett BB vs plain bearing turbos, people get hung up on where full boost is hit between BB and plain bearing turbos when under full load on the dyno... you don't see the true effect under controlled acceleration against a dyno, its when you stand on the gas midway through the revrange that it becomes truly noticeable. I know a few people who have had T3T4/T67/T04R type turbos which on shifts etc they have to really rape them to keep them on song, change to a BB equivalent and the car feels almost electric by comparison.

I'd be expecting mid/high 5000rpm range, though might be wiser to check with the RB26 brigade as it would be incredible similar - strangely enough

OK so you'd be looking for a setup capable of getting an S14 down the 1/4 mile trapping around 145mph?

I've never really thought too hard about the cause of this kind of thing when tuning with alcohol but it definitely happens. I'd say at least part of the reason would be the increased (even if just slightly) amount of volume passing through the engine and as such, through the exhaust system. We got 200rpm better spool when we tuned an RB20DET R32 running a T3/T4 on an E33 mix recently, interestingly we got an extra 40wkw on roughly the same boost level with that conservative a mixture of ethanol - and making big modifications to the fuel system wasn't needed either. I'm quite tempted to do such a tune for my Skyline...

^ Did you read his last post? I have met people who have set out to do things like what he is aiming to do, and achieved them - though as said, the 2.5litre thing could prove very restrictive in all but making the peak power level.... KB240B - one of the misleading things about comparing where full boost is reached between a 2.5 litre and a 3litre is that the engine displacement and as such, the natural non boosted torque is already 20% higher. With the 3litre you could have a LAGGIER turbo than what the GT4294 on an RB25 would be and still have the same power delivery. If it had the same amount of lag, it would smoke the RB25 for power delivery. Given the RB25 would give 500-600rpm in terms of lag, it would end up as a completely different beast in terms of peaky power.

Have you considered going for a big nasty Holset turbo? I reckon a GT4294 would be pretty seriously laggy on an RB25.... I could see it being more annoying during lag than it is fun once you get past the lag. An HX52 may prove to be a bit less laggy, not to mention just as cheap - if not cheaper

Haha cheers mate, me too - obviously The big can actuator sounds very promising... though its a fair bit of boost on the stocker RB25! The actuator is coming back from the US with a mate of mine, he actually bought it while he was over there and threw it in his luggage so no freight He left the US on Wednesday so I guess I should be able to grab it this weekend.

Fantastic, look forward to hearing how it goes - any pics or anything of progress? I may have to pull finger on the long procrastinated about trip to Oz sometime, especially if HT go over. Side by side 7s GTRs would be unreal!

That may depend on dyno.... Was this a dig at me? Not sure what you think of me but I try to help cut through the shit where possible.

Probably relevant to this thread: http://www.skylinesaustralia.com/forums/Gt...20&start=20

Nice work!! Thats very good going, my large can actuator is due to arrive this week