Turbine housing size help for Garret GT3076R

[Jaakko]

Hi, long story short:

I upgraded my turbo for Impreza STI -08 (EJ207, JDM Twin Scroll) at last summer. And supporting mods of course (fueling, exhaust, intake…). The new turbo is Garrett GT3076R (stock location, with 2,5” inlet) custom made by my local ”professional” turbo dealer/shop.

First it had way too big turbine wheel and housing (twin scroll to single). It gave huge power but only after 5000-6000rpm. We changed smaller turbine housing (11cm2, full twin scroll) and denser turbine wheel and now it’s starting to spool a little earlier but it’s also choking at redline compared to previous… It starts spooling @ 3500rpm and full boosting @5000rpm (1,6bar/23psi). So it’s still quite laggy.

I contacted scoobyclinic and asked specs for Blouch SC42 X turbo. It had almost similar specs than garret but the turbine housing was 7cm!!? Is it possible to run with so small housing without losing top-end power. My power goal is about~ 400hp.

My friend has that blouch thing and it has extremely wide and strong powerband, but he has 2.1 stroker and ethanol kit also…


Comparing:

Garrett GT3076R
Compressor: 57 / 76 mm
Turbine: 54 / 56 mm
Housing: 11cm Twin Scroll

Blouch SC42 X
Compressor: 53 / 71 mm
Turbine: 53.6 / 56.5 mm
Housing: 7cm Twin Scroll


It’s quality tuned by subaru-professional and he also said that there’s something wrong going with that turbo. I have tested all possibilities of boost-, vacuum- and pre-turbo leaks. Timing seems to be ok. Full 3” exhaust. 70mm intake and 2,5" inlet. MAF 350g/s, AFR 11.1., timing 10-20 degrees / full boost. Washed TMIC. PCV working well. No oil in boost or vacuum pipes... no extra smokes or noises...

Other strange thing is that it has internal wastegate with 0.8kg spring and there’ must to be very hard preload if you want to see boost levels going close to 1.6bar/23psi. If you preload it normally (3-5mm) it will boost only 1bar/15psi.

I tried to use stiffer 1.4kg spring also. It was boosting easier but it will not open enough at top end and the boost is collapsing. So it have to be softer one

I’m running with stock bcs, is it worth to change 3-point solenoid, will that do something magic? Oh... and the tuner changed larger restrictor pill (0,9 to 1.2mm)

* Registered users of the site do not see these ads.

[Winterhawk]

Is your goal 400 crank or wheel hp?

[Jaakko]

Whp. 370-380 will be nice also if I get it spool earlier and more streetable...

[Hyper]

I don't understand, are you comparing ancient GT turbo with a new gen billet wheel high inertia one?

for a 2.0 motor, I find Blouch 1.5 XTR is an excellent solution (its what SC46 used to be, don't know if they remarked their product range now)
alternatively EFR 67 or 71, or if you want to stay garret their new G-series, or older GTX in 28 model range

[subaru_gc8]

if the turbo is being choked at 11cm it will be even worse at 7cm. Subarus like to breath at the top so going bigger is always better. try a gtx3067 its a smaller turbo and it will spool very quickly on your car

[sluflyer06]

years ago I had a GT3076R on a built up EJ257, it had the .82AR exhaust and spool up was not a problem at all, maybe 3500 or so. I'm not sure if the intake could be a factor? I was running a 4" inlet on a rotated setup.

[Jaakko]

I was informed that blouch is basically garret. My garret is a ”hybrid” build based on 3076 body. It was builded by professional turbobuilder and i’m not exactly sure what it has inside. Something retro i think...

I’m not interested to by whole new turbo, that garrett was quite expensive... but it seems that i just have to swallow my disappointment and buy a new one.

That 2.5l motor helps to spool earlier. Bigger inlet might help also, but there’s no space on stock location bigger than 2,5-3” which i allready have.

[sense of nature]

Originally Posted by sluflyer06

years ago I had a GT3076R on a built up EJ257, it had the .82AR exhaust and spool up was not a problem at all, maybe 3500 or so. I'm not sure if the intake could be a factor? I was running a 4" inlet on a rotated setup.

I remember that car & that initial pull!
What's Up Sluflyer!! , Still around the Subbies huh?
I know it's a addiction LOL
I hope all is well!
LMk if your ever local , we'll hit up a meat!
Sorry to hi jack the thread

[Jaakko]

Originally Posted by subaru_gc8

if the turbo is being choked at 11cm it will be even worse at 7cm. Subarus like to breath at the top so going bigger is always better. try a gtx3067 its a smaller turbo and it will spool very quickly on your car

I’m not sure is it choking or is the turbine wheel too restrictive or is it overspeeding the compressor. The boost rises 1.6-1.7 bars and then drops quickly to 1.5bar. With that former bigger turbine housing and bigger turbine wheel it was just rising all the way to redline and it felt that the turbo is just warming up at 8000rpm 🙂

[AZ-GT]

So how come your local ”professional” turbo dealer/shop doesn’t seem to have a clue?

[rtv900]

Originally Posted by Hyper

are you comparing ancient GT turbo with a new gen billet wheel high inertia one?

the new billet wheels are HIGH inertia?

[HOK]

I think there is more you need to consider, first reaction would be TMIC... world of difference when I went FMIC and also your headers. if you are seeing boost dying out your entire system seems restrictive

[Jaakko]

Originally Posted by AZ-GT

So how come your local ”professional” turbo dealer/shop doesn’t seem to have a clue?

It was their first twin scroll build for subaru. They have so much work and doesn’t have any interest of helping me anymore. I have asked several times but they are just saying - get use to it.

That’s why i wrote those citate-marks

[Jaakko]

Originally Posted by HOK

I think there is more you need to consider, first reaction would be TMIC... world of difference when I went FMIC and also your headers. if you are seeing boost dying out your entire system seems restrictive

It wasn’t dying until they changed smaller turbine housing....

I have told that -08 jdm sti tmic and el headers are just fine. The main problem here is the lag. My tuner said that the fmic can even worse the lag. Of course there’s benefits at hot summer days...

[sluflyer06]

Originally Posted by Jaakko

It wasn’t dying until they changed smaller turbine housing....

I have told that -08 jdm sti tmic and el headers are just fine. The main problem here is the lag. My tuner said that the fmic can even worse the lag. Of course there’s benefits at hot summer days...

I don't honestly think a FMIC is going to add much "lag" when we're talking turbos this big, it's pushing a LOT of air. I did use a Spearco TMIC with a 20g around the 360whp mark and it was doing just fine, still with something this size, you'll get better&more consistent results with a FMIC. You don't need to get a ridiculously large core...