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Old 01-16-2020, 02:14 PM   #1
Scooby Newbie
Member#: 504930
Join Date: Aug 2019
Default Turbine housing size help for Garret GT3076R

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…


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)
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Jaakko is offline   Reply With Quote