BMW 340i B58 (F30/F31) Turbo Downpipe 3.5in – High-Flow Sports Cat or Catless De-Cat Front Pipe | Cobra Sport Performance Exhaust | BMW 3 Series 340i Down Pipe/Outlet Pipe Upgrade

BMW 340i B58 Downpipe Upgrade — High-Flow Cat or Catless Option

Unlock instant gains in response and soundtrack with this Cobra Sport turbo downpipe for the BMW 340i. Designed for the B58-powered 3 Series, this enlarged 3.5 inch (88.9 mm) front pipe replaces the restrictive factory catalytic converter from the turbo outlet to the centre section, delivering a smoother, freer-flowing exhaust path and a far more purposeful tone.

If you are chasing a sharper throttle feel, quicker turbo spool and a more engaging drive, this is the essential exhaust upgrade for remapped and stock cars alike. We have fitted this unit on customer 340i builds and feedback on fitment quality, sound and drivability has been excellent.

Why choose this Cobra Sport downpipe

• Large-bore 3.5 inch / 88.9 mm tubing for reduced back pressure and improved exhaust gas flow
• Fits from the turbocharger to the centre section, replacing the OE cat assembly
• Choice of high-flow catted version or race catless version to suit your build
• Engineered for the BMW 340i B58 turbo engine for a deeper, more aggressive note
• All required gaskets and fittings are included for a straightforward installation
• Manufacturer-backed quality from Cobra Sport for peace of mind

Ideal for tuning

This front section is a proven foundation for further upgrades and ECU calibration. The enlarged diameter and smooth routing help the B58 breathe better, supporting higher power targets while enhancing the characterful six-cylinder sound.

Choose your configuration

• High-flow catted: Increased flow with a cleaner exhaust stream, ideal for enthusiasts who want performance with added refinement.
• Catless race: Maximum flow for track and off-road builds where ultimate performance and turbo response are the priority.

Legal and compliance

Catless version: sold for motorsport and off-road use only worldwide.

High-flow catted version: replaces a factory emissions device and is not EC homologated. It may not comply with current road-going emissions rules in your region.

Professional fitting available

Want it installed properly first time? Book your fitting with MJ Modifications in Warwickshire. Email info@mjmodifications.co.uk for a quote and availability.

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What’s in the box

• Cobra Sport downpipe assembly
• Relevant gaskets and hardware

Media

Exhaust Talk Episode Two - Sports Catalyst vs De-Cat Performance Exhausts