GrimmSpeed BB450+ Turbocharger 2002-2007 WRX / 2004-2021 STI

Bolt-On Fitment. Serious Power. 

More power shouldn't mean tearing apart your engine bay. Meet the GrimmSpeed BB450+, engineered to deliver substantial horsepower gains with a true bolt-on design that works with your existing factory-style components.

Taking the place of our JB400, the BB450+ brings a new level of performance to our Subaru turbocharger lineup. At its core is a ceramic ball bearing system, replacing the JB400's traditional journal bearing design for responsive power delivery and strong performance throughout the RPM range.

The BB450+ features a billet 2618 aluminum compressor wheel and an Inconel 713C turbine wheel, paired with carefully engineered housings designed to support airflow, durability, and consistent performance under demanding conditions. An 8cm turbine housing and 0.77 A/R compressor housing help deliver a combination of midrange torque and sustained top-end horsepower.

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 more consistent wastegate operation, tighter boost control, and greater flexibility when dialing in your setup.

And the best part? It's a true bolt-on turbocharger. The BB450+ 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 a straightforward path to considerably more power.

Whether you're replacing your factory turbo or taking the next step beyond the JB400, the BB450+ delivers the performance you're after without the complications of a custom turbo installation.

QUICK SPECS

• Bearing System: Ceramic ball bearing
• Compressor Wheel: Billet 2618 aluminum
• Compressor Wheel Inducer/Exducer: 53.4mm / 67.4mm
• Turbine Wheel: Inconel 713C
• Turbine Wheel Inducer/Exducer: 49.1mm / 56mm
• Compressor Flow: 61 lbs/min
• Compressor Housing: A356 aluminum
• Compressor Housing A/R: 0.77
• Turbine Housing: HiSiMo
• Turbine Housing Size: 8cm
• Wastegate Actuator Material: 6061 aluminum
• Wastegate Base Pressure: 15 PSI (default)
• Wastegate Mounting Bracket: Straight, 6-gauge zinc-plated steel
• Adjustable Base Pressure Range: 3–26 PSI with included spring combinations
• Boost Control Compatibility: 3-port and 4-port configurations
• Installation: Factory-location bolt-on; no cutting or custom fabrication required

Dyno Testing: Putting the BB450+ to Work

We put the BB450+ to the test against the factory VF48 and our previous JB400 turbocharger to see how the new 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.

BB450+ Dyno Results:

• Peak Wheel Horsepower: Approximately 485 WHP

• Peak Wheel Torque: Approximately 460 lb-ft

• Horsepower Gain vs. JB400: Approximately +90 peak WHP

• Torque Gain vs. JB400: Approximately +45 peak lb-ft

But the real advantage becomes clear when looking beyond peak numbers.

Compared to the JB400, the BB450+ delivers stronger horsepower and torque through much of the RPM range, with an increasingly noticeable advantage as engine speed climbs. At approximately 6,500 RPM, the BB450+ maintains around 480 WHP, compared to roughly 370 WHP from the JB400.

That's a difference of approximately 110 WHP at the same engine speed, demonstrating just how much more power the BB450+ carries toward redline.

The result is a turbocharger that combines substantial midrange performance with a considerably stronger top end, 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.

Stock Motor Testing: 93 Octane vs. E60

We also put the BB450+ to the test on a 2013 Subaru STI with a factory stock engine, giving us a closer look at its performance on a more conventional setup. The vehicle featured a stock intake, GrimmSpeed Top Mount Intercooler, GrimmSpeed Equal Length Header, up-pipe, and catted downpipe.

Running on 93 octane pump gas, the BB450+ produced approximately 378 WHP and 338 lb-ft of wheel torque. Switching to an E60 ethanol blend increased output to approximately 420 WHP and 368 lb-ft, demonstrating the additional performance available with different fueling configurations.

Both configurations demonstrated strong midrange torque and horsepower that continued building toward redline. These results offer a closer look at how the BB450+ performs on a daily-driven STI with stock engine internals and select supporting modifications, highlighting its power delivery across different fueling configurations.

How It Stacks Up: A Closer Look

When compared directly against the BB500 and BB550+, the BB450+ demonstrates its strength in earlier torque delivery and responsive midrange performance. While the larger BB550+ ultimately produces greater peak horsepower, the BB450+ develops power sooner, delivering an impressive balance of acceleration and sustained horsepower throughout the RPM range.

For STI drivers prioritizing responsive power delivery and a broad, usable powerband, the BB450+ makes a compelling case.

Redesigned Wastegate Actuator: Precision Boost Control

The BB450+ 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 BB450+ ships with a 15 PSI base spring and an additional spring pack, allowing you or your tuner to adjust base pressure to suit your performance goals. An included reference chart makes selecting the proper spring combination 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.

FITMENT

2002-2007 WRX

2004–2021 STI

Installation Note: The BB450+ 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.