BMW B58 Decat Downpipe 4 Inch Polished Stainless - M140i M240i 340i 440i - High Flow Catless, Stage 2/Remap Ready (Off-Road Use)

BMW B58 Race Down Pipe - M140i, M240i, 340i, 440i - 4 inch Polished Stainless

Free the B58 and let the turbo breathe. This large bore 4 inch polished stainless front pipe replaces the restrictive factory primary catalyst on the B58-powered M140i, M240i, 340i and 440i. Expect quicker turbo spool, stronger mid-range punch, sharper throttle response and a deeper motorsport tone when paired with appropriate software. If you are building a fast road or track-only BMW with a calibration to match, this is the essential exhaust hardware upgrade.

We have installed this on our own B58 projects and many customer cars. Feedback has been superb for sound quality, fit and finish, and drivability when mapped. The polished stainless construction looks premium and resists corrosion, while the big-bore tube minimises back pressure for maximum flow. Ideal as the foundation for stage two style tuning with an ECU calibration.

Key reasons to choose this B58 turbo front pipe

• Large bore 4 inch design for superior gas flow and reduced back pressure
• Polished stainless steel construction for durability and a clean finish
• Faster spool and improved throttle response on the B58 single turbo engine
• Perfect hardware for remapped and software-tuned setups
• Deeper, more assertive exhaust character under load
• Proven on our in-house builds and by happy MJ Modifications customers

Vehicle compatibility

• BMW M140i - B58 engine
• BMW M240i - B58 engine
• BMW 340i - B58 engine
• BMW 440i - B58 engine

Performance and tuning notes

This free-flow front section is best paired with an appropriate ECU calibration for the B58 to optimise boost control and fuelling. Expect a noticeable gain in response and a stronger pull through the rev range when combined with suitable software and supporting mods. For track and motorsport builds only.

Installation and support

Professional fitting is recommended. MJ Modifications offers installation at our Warwickshire workshop. To request a fitting quote or booking, email info@mjmodifications.co.uk.

Legal notice

This product removes the primary catalytic converter and is intended for off-road, race, or track use only where regulations permit. Check local laws before purchase and installation.

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