MAD BMW Toyota B58 Fat Boy 5" Catless Downpipe M240 340 440 Supra

Meet the MAD B58 Fat Boy 5" Catless Downpipe. With a massive 5-inch diameter, it provides unrestricted exhaust flow that slashes backpressure and unlocks more horsepower and torque — while the catless design and big bore deliver a deeper, far more aggressive sound. Premium stainless steel construction handles the heat and pressure of hard driving for years.

Expect up to a 30 HP increase on a tuned B58 with the stock turbo, and even more on an upgraded turbo. Installation is straightforward with basic hand tools.

Features

• Massive 5" catless design for maximum flow and sound.
• Compatible with right- and left-hand-drive vehicles.
• Smooth bends for maximum airflow with no drone, plus a flex section.
• Lifetime warranty on defects and fitment; 90-day return; ships in 1–2 business days; spot-on fitment.

Fitment

• 2015+ BMW M240i & xDrive
• 2016–2019 BMW 340i & xDrive
• 2020–2024 BMW M340i & xDrive (does not fit 2025+)
• 2016+ BMW 440i, 540i & 740i (& xDrive)
• 2017–2024 BMW X3 M40 & X4 M40 (G01/G02)
• 2019+ BMW X5 40i (G05), X7 40i (G07) & Z4 M40i (G29)
• 2019+ Toyota Supra 3.0L

Emissions disclaimer: This product is not legal for sale or use on pollution-controlled vehicles operated on public roads and is intended for off-road, race, or closed-course competition use only. You are responsible for compliance with all applicable emissions laws; use on public roads may violate the Federal Clean Air Act (42 U.S.C. § 7522) and similar state laws. Please check your local laws before purchase and installation.

Ships from our Vancouver shop — KORE SPEED is proudly Canadian-owned, with no surprise cross-border duties for Canadian buyers. Questions on fitment? Email support@korespeed.com.