SteamSpeed STX 76R Ball Bearing Turbo for BMW N55 Twin Scroll PWG

note: these units are made on demand, so allow 2-4 for assembly and shipping.

The SteamSpeed STX 76R Ball Bearing Turbo for BMW N55 PWG is a complete turbo upgrade for your BMW featuring a dual ceramic ball bearing cartridge and a custom GTX3076R sized compressor and turbine wheels.  This turbo is designed to provide early torque for a more stock-like response but with loads more power and power holding throughout the power band instead of falling off on the top end.

This turbo is designed to work well with basic mods.  With a larger front mount intercooler, downpipe, inlet, charge pipe, and low-pressure fuel pump, our testing shows roughly a 20% power gain vs the just the bolt-ons and the stock turbo with just 16 psi of boost.  The STX 76R compressor wheel does flow over 65 lbs/min over 25 psi, so it is plenty capable of making even more power than that.  With sufficient fueling, the STX 76R is capable of making 550-600 whp.

The STX 76R installed on a N55 on an engine stand:

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.

Modifications:
"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

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.

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

Conclusion:
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.

Furthermore:
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.