OneFastShop B58 Downpipe – Unlocking the True Power of Your BMW and Supra

The BMW B58 engine has quickly become one of the most celebrated turbocharged inline-six powerplants of the modern era. From its debut in the F30 340i to its presence in the latest G-Series M340i, M440i, and even the Toyota Supra A90, the B58 is renowned for its balance of reliability, responsiveness, and tuning potential.

Yet, from the factory, one critical component limits what this engine can deliver: the restrictive downpipe. That is why enthusiasts consistently turn to the OneFastShop B58 4.5” Catless Downpipe — a proven upgrade that removes factory bottlenecks, unlocks horsepower, and transforms the sound and character of the car.

What is a Downpipe and Why Upgrade It?

The downpipe connects the turbocharger to the exhaust system. On turbocharged vehicles like the B58, it is responsible for directing hot exhaust gases away from the turbine. The stock BMW downpipe includes a dense catalytic converter, designed to reduce emissions but at the cost of airflow.

This restriction creates backpressure, slows turbo spool, and limits tuning potential. Replacing the factory unit with the OneFastShop 4.5” Catless Downpipe allows the exhaust gases to exit more freely, dramatically improving flow. The result is faster turbo response, increased horsepower, and a far more aggressive exhaust tone.

Key Benefits of the OneFastShop B58 Downpipe

Sharper Turbo Response
With less restriction, the turbo can spool more quickly. Drivers notice improved throttle response and reduced turbo lag, making the car feel more immediate and connected.

Increased Horsepower and Torque
With proper tuning, gains of 25–30 horsepower are achievable. Beyond peak numbers, the powerband becomes stronger, smoother, and more consistent under load.

Aggressive Exhaust Note
The downpipe produces the most noticeable transformation in sound. Owners describe a deeper, sportier tone, paired with audible turbo spool and crackles that simply are not present with the stock system.

Support for Future Upgrades
Whether planning higher boost levels, larger turbos, or custom tunes, the OneFastShop B58 Downpipe provides the airflow foundation needed for reliable big-power builds.

Premium Construction and Design

The OneFastShop B58 Downpipe is not only about performance but also durability and precision fitment. It is manufactured to withstand the high heat and pressure of turbocharged applications without compromise.

• Material: 304-grade stainless steel for superior corrosion resistance

• Flanges: CNC-machined for perfect sealing and alignment

• Tubing: 4.5” mandrel-bent design ensures consistent diameter and maximum flow

• Welding: Hand TIG-welded for structural integrity and long-term reliability

Each unit is built to exacting standards, ensuring the installation is straightforward and the performance results are consistent across all B58 platforms.

Easy Installation – Direct Bolt-On Fit

The OneFastShop B58 Downpipe is designed as a direct bolt-on replacement. It uses the factory mounting points and hardware, requiring no cutting or welding. The process can be completed with standard tools, making it accessible for experienced enthusiasts or trusted performance shops.

• Fits both left-hand drive and right-hand drive vehicles

• Compatible with the OEM exhaust system

• Seamlessly integrates with most aftermarket exhaust setups

This ensures maximum flexibility whether keeping the rest of the system stock or pursuing a complete exhaust upgrade.

Proven on the Street and Track

Drivers who have installed the OneFastShop B58 Downpipe consistently report the same improvements:

• Noticeable gains in both horsepower and torque with only a simple tune

• A much more engaging exhaust note, transforming the personality of the car

• Reliable performance under extended high-heat conditions on track days

These real-world experiences confirm what the technical specifications suggest: the downpipe is a high-value modification that dramatically enhances the driving experience.

Vehicle Compatibility

The OneFastShop B58 4.5” Catless Downpipe fits a wide range of BMW and Toyota models equipped with the B58 engine, including:

• Toyota Supra A90 (2020–2024)

• BMW 2 Series – M240i (2017–2024)

• BMW 3 Series – 340i (2016–2018), M340i (2020–2024)

• BMW 4 Series – 440i (2017–2024), M440i (2021–2024)

• BMW 5 Series – 540i (2017–2023)

• BMW 6 Series – 640i (2018–2019)

• BMW 7 Series – 740i, 745e (2016–2022)

• BMW 8 Series – 840i (2020–2024)

• BMW X3 M40i (2018–2024)

• BMW X4 M40i (2019–2024)

• BMW X5 40i / 45e (2019–2024)

• BMW X6 40i (2020–2022)

• BMW X7 40i (2019–2022)

• BMW Z4 M40i (2020–2024)

This broad compatibility ensures that nearly every B58 owner can benefit from the upgrade.

Important Considerations

The OneFastShop B58 Downpipe is offered in race configuration (catless). It is intended for off-road and track use only. This product may not comply with emissions standards or be legal for street use in certain regions. Customers are advised to verify local laws and regulations prior to installation.

Final Thoughts – The Best Upgrade for the B58

The B58 engine already delivers an impressive balance of power and refinement, but the stock downpipe holds it back. The OneFastShop B58 4.5” Catless Downpipe provides one of the best performance-per-dollar improvements available. With significant gains in horsepower, torque, throttle response, and sound, it is the perfect starting point for any enthusiast looking to unlock the full potential of their BMW or Supra.

Available now at OneFastShop – $250 (Save 17% off retail $300). In Stock and Ready to Ship.