GrimmSpeed's New BB450+ & BB550+ Turbos: Dyno Results & First Look

GrimmSpeed BB450+ & BB550+ Turbochargers: New Dyno Results Reveal Impressive Performance Gains

GrimmSpeed has offered an early look at its next generation of Subaru STI turbochargers, introducing the upcoming BB450+ and BB550+. Designed to replace the existing JB400 and BB500, these new turbochargers aim to deliver increased horsepower, improved performance characteristics, and updated technology for enthusiasts looking to take their STI builds to the next level.

GrimmSpeed recently shared results from its development testing, providing a first look at how both turbochargers perform against their predecessors. While complete specifications and release details have yet to be announced, the initial dyno results highlight some substantial improvements.

Here's a closer look at what GrimmSpeed has revealed and what these new turbochargers could mean for Subaru STI owners.

A Closer Look at GrimmSpeed's Turbocharger Testing

To evaluate the upcoming turbochargers, GrimmSpeed used a modified 2020 Subaru STI equipped with a built engine featuring upgraded rods and pistons, Stage 3 supporting modifications, a front-mount intercooler, 1300cc fuel injectors, and E85 fuel.

Testing was conducted on a Mustang Dyno, with performance comparisons involving five different turbochargers:

• Factory Subaru VF48

• GrimmSpeed JB400

• GrimmSpeed BB450+ (upcoming)

• GrimmSpeed BB500

• GrimmSpeed BB550+ (upcoming)

Rather than evaluating peak horsepower alone, the testing examined how horsepower and torque developed throughout the RPM range. This distinction is important because two turbochargers producing similar peak horsepower can offer significantly different driving characteristics depending on their power delivery.

The results suggest that GrimmSpeed's newest offerings aren't simply focused on producing higher peak numbers. Each turbocharger introduces meaningful changes to how power is delivered.

GrimmSpeed BB450+: More Horsepower Across the Powerband

The upcoming BB450+ will replace GrimmSpeed's existing JB400 turbocharger, bringing both mechanical improvements and a substantial increase in power output.

One of the most significant updates is the transition from the JB400's conventional journal bearing design to a ceramic ball bearing system.

Ball bearing technology can reduce rotational friction compared with traditional journal bearing designs. However, actual turbocharger response depends on several factors, including the overall rotating assembly and turbine configuration.

Beyond the updated bearing technology, the BB450+ demonstrated considerable horsepower and torque improvements during GrimmSpeed's testing.

BB450+ vs. JB400 Dyno Results

Figures are approximate and reflect GrimmSpeed's E85 test configuration.

The BB450+ delivered approximately 90 additional peak wheel horsepower and 45 additional lb-ft of peak wheel torque compared with the JB400.

Perhaps more importantly, the BB450+ maintained a significant advantage throughout much of the powerband.

At approximately 6,500 RPM, the BB450+ produced around 480 WHP, compared with just 370 WHP from the JB400. That's an improvement of approximately 110 wheel horsepower at the same engine speed.

This substantial difference in upper-RPM output suggests that the BB450+ could be particularly appealing to enthusiasts seeking stronger acceleration through the higher gears without focusing exclusively on maximum peak horsepower.

With increased output across much of the RPM range and a new ceramic ball bearing design, the BB450+ represents a significant evolution of GrimmSpeed's existing JB400 platform.

GrimmSpeed BB550+: Greater Top-End Power Potential

For enthusiasts seeking even greater horsepower, the upcoming GrimmSpeed BB550+ takes a different approach.

Developed as the successor to the BB500, the BB550+ features a larger turbocharger design focused on delivering substantially more horsepower at higher engine speeds.

Despite its increased size, GrimmSpeed's testing suggests that the BB550+ retains much of the BB500's lower-RPM performance while delivering significantly greater output as engine speed increases.

BB550+ vs. BB500 Dyno Results

Figures are approximate and reflect GrimmSpeed's E85 test configuration.

The BB550+ generated approximately 530 wheel horsepower, representing a 70 WHP increase over the BB500.

The difference becomes especially noticeable above 5,200 RPM, where the BB550+ begins outperforming the BB500 in horsepower. Its advantage continues increasing toward redline, where the newer turbocharger maintains more than 520 WHP at approximately 6,500 RPM.

However, the additional top-end horsepower comes with a change in torque delivery.

The BB500 achieves peak torque around 4,600 RPM, while the larger BB550+ reaches its peak closer to 5,500 RPM. This indicates a shift toward higher-RPM performance, with some compromise in the lower portion of the powerband.

Interestingly, the BB550+ still develops a noticeable increase in torque around 4,500 RPM, a characteristic also observed with the BB450+ and BB500.

For STI owners prioritizing maximum horsepower while retaining a usable midrange, these initial results are particularly promising.

The BB550+ May Have Even More Power Available

One of the most interesting details from GrimmSpeed's testing is that the BB550+ may not have reached its full performance potential.

According to GrimmSpeed, the 1300cc fuel injectors installed on its test vehicle became the limiting factor at approximately 530 WHP.

As a result, testing was capped at 27 PSI of boost.

GrimmSpeed's engineering team estimates that the BB550+ could support approximately another 5–6 PSI of boost before operating outside its efficiency range.

This suggests that additional horsepower may be achievable with an appropriately upgraded fuel system and supporting modifications.

However, it's important to distinguish these engineering estimates from verified dyno results. GrimmSpeed has not yet published testing demonstrating the BB550+'s maximum output at those higher boost levels.

Even at the tested 27 PSI, the BB550+ demonstrated a substantial improvement over its predecessor.

BB450+ vs. BB550+: Which Turbocharger Is Right for Your STI?

Although both turbochargers represent upgrades over their respective predecessors, their performance characteristics indicate that they may appeal to different types of STI builds.

Choose the BB450+ for a Broad, Strong Powerband

Based on GrimmSpeed's initial results, the BB450+ appears well suited to enthusiasts seeking a balance between strong midrange performance and increased upper-RPM horsepower.

Its advantages include:

• New ceramic ball bearing technology

• Approximately 485 WHP on GrimmSpeed's test vehicle

• Increased torque and horsepower compared with the JB400

• Strong horsepower retention toward redline

For enthusiasts who prioritize usable performance throughout the RPM range, the BB450+ looks like a compelling option.

Choose the BB550+ for Maximum High-RPM Performance

The BB550+ appears better suited to builds where greater peak horsepower and sustained upper-RPM performance are the primary objectives.

Its advantages include:

• Approximately 530 WHP during initial testing

• Substantial horsepower improvements over the BB500 above 5,200 RPM

• Strong upper-RPM performance while retaining useful midrange torque

• Additional estimated boost capacity that has not yet been fully explored through published testing

The trade-off is a later peak-torque delivery compared with the BB500, something drivers should consider when selecting a turbocharger for their intended use.

Ultimately, the better choice will depend on the vehicle's supporting modifications, fueling, intended use, and desired powerband.

What Else Do We Know About the New GrimmSpeed Turbochargers?

While the preliminary performance figures are encouraging, GrimmSpeed has not yet revealed every detail about the BB450+ and BB550+.

Additional technical specifications, engineering details, and official release information are expected to be announced as the new turbochargers approach launch.

It's also important to recognize that the published dyno results were achieved on a heavily modified STI running E85. Actual horsepower and torque figures will vary depending on engine configuration, fuel, boost pressure, tuning, and other supporting components.

These results should therefore be viewed as a demonstration of the turbochargers' capabilities under GrimmSpeed's specific testing conditions rather than guaranteed output figures for every application.

Final Thoughts: An Exciting New Chapter for GrimmSpeed Turbochargers

GrimmSpeed's preliminary testing suggests that the BB450+ and BB550+ could represent substantial upgrades for Subaru STI enthusiasts.

The BB450+ delivers an impressive combination of increased horsepower, stronger torque output, and updated bearing technology, while the BB550+ raises the bar for higher-RPM performance with more than 520 wheel horsepower maintained near redline.

Perhaps the most encouraging takeaway is that these improvements extend beyond peak horsepower. Both turbochargers demonstrate meaningful differences in power delivery compared with the models they're designed to replace.

With additional specifications and official release details still to come, the BB450+ and BB550+ are two upcoming products worth watching for anyone considering a turbocharger upgrade for their Subaru STI.

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