SteamSpeed N55 STX 76R BB Turbo Initial Testing Result

Feb 8, 2018
Focus RS, Impreza RSti
I haven't posted for a long while, but we have been developing and testing an all-new N55 ball-bearing turbo for N55 called the STX 76R.

What it is:
It is a stock location complete turbo replacement for the N55 with a dual ceramic ball-bearing cartridge which some may consider a "stage 2" sized turbo. We designed and developed all-new housings, which means it is not simply a remanufactured OE turbo with larger wheels. The turbine housing is an advanced twin-scroll design with a new cast manifold. The turbo is also stock-location meaning it is designed to fit like an OEM turbo and all other bolt-ons designed to work with the OEM turbo, will also bolt-up to this turbo.

Turbo Specs:
- Compressor wheel: 58mm inducer, 76mm exducer, flows ~67 lbs/min
- turbine wheel: 60mm inducer, 55mm exducer
- compressor housing, new casting, stock-style
- turbine housing, new casting, high-performance twin-scroll, +sized A/R vs stock


Car Under Test:
This data is from a 135i with PWG-style N55. We took a stock car with the base MHD map, measured performance, added basic standard bolt-ons, measured again with the MHD 2+ tune, and finally added the STX 76R and measured again after tuning for the turbo. The idea was to take a stock N55 car running pump gas and a conservative amount of boost, and add a minimum set of bolt-ons to support a turbo, and then add the STX 76R.


"Stage 2" upgrades: larger front mount intercooler, catless downpipe, charge pipe, inlet, and MHD stage 2+ tune. Everything else was stock including fuel pump, ect.
Post turbo modifications: all of the above + STX 76R + tune

The turbo tune was done by Zack at 22rpd on their DynoCom dyno with pump gas and ~15 psi target. Zack is a long time BMW tuner well-known for high-power turbo builds on E36 and E46 cars.

Stock: 310 whp, 307 ft*lbs
Stage 2+: 366 whp, 436 ft*lbs
With STX 76R+ turbo: 429 whp, 416 fr*lbs



The turbo basically accomplished what it was designed to do, respond quickly, and make much better power than the stock turbo. With a few boltons and the SteamSpeed STX 76R, a stock N55 car made another 120 whp, or around 40% more power. As compared to the car with boltons, the car made another 60 whp, or around a 20% gain. Our turbine housing also made a nice torque and powerband. Our new housings also allowed the powerband to hold on much longer to red where you would normally see turbos with stock housings fall off.

As we continue testing on other cars, we found that fueling was limiting this setup, and adding a Walbro 450 LPFP, we were able to see around 450 whp and 450 ft*lbs on pump gas and 16 psi, so we recommend doing that upgrade as well as the basic stage 2 stuff.

Next up, we'll push it to the 20-25 psi range on pump gas to hit closer the turbo's peak flow. The turbo would flow the most around 25-30 psi, but that will more than what pump gas can provide.
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Lieutenant General
Staff member
Aug 11, 2017
E89 Z4 35i, F10 535d
Suggest looking at the 535lph pump instead of the 450, given what you are looking to do. See the thread hear on those developments. You'll likely have a better chance of getting the fuel you need without having the swap out the EKP. Nice post ^^^^ !

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Nov 2, 2017
135i N55 DCT; PS2
Thanks for the post and nice results. Always nice to see new products coming out, especially for pwg n55!

Do you have any logs of the dyno runs? Would be nice to see them.
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