GrimmSpeed BB550+ Turbocharger - Subaru WRX 2002-2007/STI 2004-2021
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Bolt-On Fitment. Big Power.
More horsepower. More top-end performance. No need to tear apart your engine bay. Meet the GrimmSpeed BB550+, engineered to deliver serious power with a true bolt-on design that works with your existing factory-style components.
Building on everything we learned from the BB500, we've combined proven engineering with our latest turbocharger technology to develop the BB550+ for next-generation STI performance. Featuring a ceramic ball bearing system, the BB550+ delivers substantially greater horsepower at higher RPM while maintaining strong midrange performance.
At its core is a billet 2618 aluminum compressor wheel and an Inconel 713C turbine wheel, paired with carefully engineered housings designed for durability and high-flow performance. A larger 10cm turbine housing and 0.77 A/R compressor housing support the BB550+'s increased power potential, allowing it to continue building horsepower well into the upper RPM range.
We've also completely redesigned the wastegate actuator, incorporating a billet aluminum body, dual-port design, and heavy-duty steel mounting bracket. Together, these improvements deliver smoother wastegate operation, tighter boost control, and greater flexibility when dialing in your setup.
And like the BB450+, the BB550+ is a true bolt-on turbocharger. It retains the factory mounting location and is designed to work with stock-style connections and existing compatible supporting components. No cutting, custom fabrication, or extensive modifications under the hood required. Just serious power without the complications of a custom turbo installation.
For drivers ready to push their STI further, the BB550+ delivers significantly greater top-end performance while retaining much of the lower-RPM response of its predecessor.
Quick Specs
- Bearing System: Ceramic ball bearing
- Compressor Wheel: Billet 2618 aluminum
- Compressor Wheel Inducer/Exducer: 57.53mm / 71.43mm
- Turbine Wheel: Inconel 713C
- Turbine Wheel Inducer/Exducer: 55mm / 60mm
- Compressor Flow: 73 lbs/min
- Compressor Housing: A356 aluminum
- Compressor Housing A/R: 0.77
- Turbine Housing: HiSiMo
- Turbine Housing Size: 10cm
- Wastegate Actuator Material: 6061 aluminum
- Wastegate Mounting Bracket: Straight, 6-gauge zinc-plated steel
- Boost Control Compatibility: 3-port and 4-port configurations
- Wastegate Base Pressure: 15 PSI (default)
- Adjustable Base Pressure Range: 3–26 PSI with included spring combinations
- Installation: Factory-location bolt-on; no cutting or custom fabrication required
Dyno Testing: Putting the BB550+ to Work
We put the BB550+ to the test against the factory VF48 and our previous BB500 turbocharger to see how the larger design performs throughout the RPM range.
Testing was conducted on a Mustang Dyno using a 2020 Subaru STI equipped with a built rod-and-piston engine, front-mount intercooler, 1300cc injectors, and E85 fuel.
The results speak for themselves.
BB550+ Dyno Results:
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Peak Wheel Horsepower: Approximately 530 WHP
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Peak Wheel Torque: Approximately 465 lb-ft
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Horsepower Gain vs. BB500: Approximately +70 peak WHP
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Torque Gain vs. BB500: Approximately +15 peak lb-ft
The real advantage becomes clear when examining the entire power curve.
While the BB500 develops torque earlier, the BB550+ trades a modest amount of lower-RPM output for considerably greater top-end performance. The BB550+ overtakes the BB500 in horsepower at approximately 5,200 RPM, with the gap continuing to widen as engine speed increases.
At approximately 6,500 RPM, the BB550+ maintains more than 520 WHP, compared to roughly 450 WHP from the BB500. That's an advantage of more than 70 WHP at the same engine speed, demonstrating the BB550+'s ability to carry substantial power toward redline.
And despite its larger design, the BB550+ still develops a noticeable torque bump around 4,500 RPM, helping preserve responsive midrange performance for a stock-location turbocharger.
There's even more potential beyond these results. Our test vehicle's 1300cc injectors limited fuel delivery at approximately 530 WHP, so we capped the pull at 27 PSI of boost. Our engineering team estimates the BB550+ has another 5–6 PSI of boost available before leaving its efficiency range, meaning the horsepower shown here doesn't necessarily represent the turbocharger's maximum capability. The result is a turbocharger that delivers considerably more high-RPM horsepower without an equally dramatic reduction in low-end performance, all while retaining the convenience of a factory-location, bolt-on design.
*Dyno results reflect the specific test vehicle, supporting modifications, E85 fuel, and tuning. Individual results will vary.
How The 550+ Stacks Up: More Power at Higher RPM
The BB550+ demonstrates its advantage as engine speed climbs, producing substantially greater horsepower than both the BB450+ and BB500 in the upper RPM range. While the smaller turbos develop torque earlier, the BB550+ continues building power, ultimately reaching approximately 530 WHP and maintaining strong output toward redline.
For STI drivers chasing maximum horsepower and sustained high-RPM performance, the BB550+ delivers a distinct advantage.
Redesigned Wastegate Actuator: Precision Boost Control
The BB550+ features our newly engineered billet aluminum, dual-port wastegate actuator, designed for smoother operation, more consistent boost pressure, and precise control throughout the RPM range.
We also developed a heavy-duty mounting system using a straight, 6-gauge zinc-plated steel bracket. Unlike thinner, bent brackets that can flex under load, this rigid design keeps the actuator rod properly aligned with the wastegate arm, reducing the potential for binding, inconsistent boost pressure, and long-term bracket fatigue.
For greater tuning flexibility, each BB550+ ships with a 15 PSI base spring and an additional spring pack, allowing you or your tuner to adjust base pressure from 3–26 PSI using different spring combinations. An included spring selection guide makes choosing the proper configuration straightforward.
The actuator's dual-port design supports both traditional 3-port and advanced 4-port boost control configurations. With a compatible 4-port setup, pressure can be applied to both sides of the internal diaphragm for finer control and greater flexibility at higher RPM.
Fitments
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2004–2021 Subaru STI
- 2002-2007 Subaru WRX
Installation Note: The BB550+ is designed for direct bolt-on installation without cutting or custom fabrication. Proper ECU tuning is required to ensure safe operation and optimal performance. Additional supporting modifications may be necessary depending on your vehicle's setup and performance goals.
