Gt3076 6 Blade Vs 7 Blade, Did Research But More Inside

[HIKAR1]

Hi lads,

I've got the 7 blade gt3076 with the t04s 0.7 a/r compressor cover on it, 0.82A/r rear housing ext gated. I have used this turbo on my previous RB25DET and made 292rwkw @18psi on the state's lowest reading dyno (C-Red @ W.A). I'm currently doing a RB30DET conversion with this same turbo and after lot of research (sau, hardtune, nasioc etc) I find that there is not a conclusive answer to the difference between the real GT3076R (6 blade) vs the Gt3076 with 7 blade T04S compressor cover on it beside "the 7 blade old design chokes flow at high boost, it acts like a brake". I have looked the compressor maps (attached below) and there isn't much variation point to point between the pressure ratio and the air flow between the 6 blade and 7 blade, they also flow to about 53lb/min at 68% efficiency.

Question is, can experts point out where I did wrong/right to verify the 7 blade (52T) is inferior to the real 6 blade gt3076r (56T)?

What I'm aiming is like al's or cubes setup but externally gated, ~350rwkw with E42.5 (50% E85 and 50% 98 ron) with the intention of full boost by 3000rpm and to max out the AFM, turbo and injectors. The setup is:

RB30DET

9:1 CR 86.5mm CP pistons

Spool conrod

My current 7 blade turbo

Tomei poncams

RB25DET head vct enabled

Power FC

Steam pipe exhaust manifold

Greddy Intake manifold

760cc JECS Injectors

Z32 AFM

The RB25 made full boost by 4000rpm which was great for barbagallo long track but as soon as I go short track or enter rally sprint events (very tight course) the lag really slowed me down.

Also did a quick calc based on the real GT3076R RB30DET setup like al's and cubes; 3L, 7000rpm, VE 92%, Boost: 18psi gives a pressure ratio of 2.2 and 53lb/min air flow (see no corrections air temp etc are made here) plots to the right side of the 65% efficiency range but these guys are making ~330rwkw happy power.....

What do you think?

[GTSBoy]

The comp maps are not similar at all. The 52T wheel makes it to 47 lb/min (on the max efficiency line) at a PR of 3.0. The 56T is on max efficiency line at the same mass flow at a PR of 3.75. ie, the 56T likes high boost to make the flow.

If you have an engine that needs the boost to make the flow, then the 56T will be more efficient and further from the surge line. If you have a bigger (flowing) engine that doesn't need to run so much boost, then the 52T will suit better.

[Dale FZ1]

There are technical and practical reasons why the 6 bladed BCI-18 compressor is a better thing. The maps point the way forward, but GTSBoy makes a valid comment.

I suspect Discopotato03 will wade into this.

Meanwhile why not run the unit you have and see how it performs on the 30DET.

[HIKAR1]

I would but it is more of like doing it right first time because I really cbf pulling turbo in and out haha.

[Dale FZ1]

Checking stated aims, I'd question why you'd want to max either the AFM or injectors. Decide on the airflow (ie power) target, and gear both the fuel system and ECU capability (thinking peak measuring ability of the AFM) to suit.

[HIKAR1]

Ok, bit the bullet and made a quick decision. Just bought a Gt35r near new condition, that really escalated quick but now I can sleep.

Why I said I want to either max out the injector or afm or turbo was because either one of them will max out at 500rwhp

On the pic: 7 Blade GT3076r, Gt3582r (yay!) and blitz kkk450r

Edited March 24, 2014 by kliono

[GTScotT]

A 35R is a good unit but there is one fundamental problem with what you just did.. You started building to have more sting on shorter tracks.. You opted to increase displacement to do this, and took a step up in that department.. Now you have also taken a step up in turbo and are likely in a similar position to before, just with more power to boot.

What was the thought process that lead to this?

[hypergear]

when both compressors are maxed. Garrett 6 pair blade 76mm 56t actually make slightly more power with better response then the 7 pair 76mm compressor or referred as 60-1.

[Dale FZ1]

For track use, I'd suggest that a 1.06 turbine housing on the GT30 is a reasonable way to go, with more efficient turbine flow and reduced backpressure for better scavenging and reduced retained heat. And the 60-1 compressor while not ultimately as efficient still isn't a bad thing.

Arguably the best thing about using the GT35 turbo is that you've achieved more efficient turbine flow and would consider using less boost to achieve the power target but not smack into traction/driveability issues that Scott is alluding to. And if you're thinking of trying to use 500rwhp in a 2wd chassis and effectively get it to the ground on short/tight tracks then good luck.

[R31Nismoid]

To the original question GTSBoy hit the nail perfectly.

The other problem the 7-blade wheel had, was compressor surge in the lower RPM on at least a RB25. I had one of these 7-blade devils back 8 years ago, they were called a GT3040 then, on a RB25 (tidied up head/ slight cc increase and that's about it)... And low RPM surge was a particularly annoying problem around 1900rpm. Tried to alter the tune a few times and just couldn't get it right and ended up going RB26 due to a few factors.

Still made good power, 270/280rwkw on around 17psi so similar to you, much more boost didn't net a whole lot of gain on PULP however. We did crank it up to 24psi and put 104 Sunoco through it for an Autosalon haha, walked away with 369rwkw so it still performed at higher boost levels but it required the fuel to do it.

[GTScotT]

The other problem the 7-blade wheel had, was compressor surge in the lower RPM on at least a RB25. I had one of these 7-blade devils back 8 years ago, they were called a GT3040 then, on a RB25 (tidied up head/ slight cc increase and that's about it)... And low RPM surge was a particularly annoying problem around 1900rpm. Tried to alter the tune a few times and just couldn't get it right and ended up going RB26 due to a few factors.

I was sure that you did have an actual GT3040? Did you end up disassembling the turbo to find it was a 7 blade 76mm compressor?

[discopotato03]

Yeah GT"3040" means GT30 turbine with GT40 82mm compressor wheel . These were originally an older HKS spec turbo and the difference between theirs and the Garrett marketed version was the compressor trim - 50T vs 56T . You basically got a bit more airflow than a GT3037/GT3076R 56T with the 50T 3040R . Even when HKS went to a cropped GT35 turbine in their GT"3240R" they kept the 82mm compressor trim at 54 .

And yep I reckon a larger turbine housing on the original turbo would have been the simple and cost effective option . From Garretts maps you get a healthy flow increase with the GT30 turbine going from 0.82 to 1.06 turbine housings , logical step with an RB30 in mind .

If the ask was 330+ I reckon the way to keep the turbo responsive is to increase the housing size because the rotating groups inertia doesn't increase like it will with larger wheels particularly the turbine . Garrett already gives you a 0.70 AR compressor housing on those "7 blade" GT3076Rs so changing turbine housings if required is straightforward .

One further , I'm not so sure the 7 blade wheel is a T04S . From memory their blades have a leading tip if you know what I mean where the S and 60-1 series had perpendicular blades . The 7 blade one could be TB41 series but whatever . GTX is the foreseeable future .

A .

[GTScotT]

One further , I'm not so sure the 7 blade wheel is a T04S . From memory their blades have a leading tip if you know what I mean where the S and 60-1 series had perpendicular blades . The 7 blade one could be TB41 series but whatever . GTX is the foreseeable future .

Stao seemed pretty confident its a 60-1, I wonder if he can confirm in any better detail?

[discopotato03]

60-1 or from memory 409535-1 is a 76mm 60T wheel . I think there were half a dozen trim versions of that compressor with 60T being the largest .

A .