Description
High Flow Engineering B58 Gen 1 Downpipe 4.5″ Decat Upgrade
Unlock greater performance from your BMW B58 Gen 1 engine with the HFE 4.5″ Decat Downpipe. Designed for models such as the M140i, M240i, M340i and M440i, this oversized high-flow downpipe replaces the restrictive factory catalytic section, significantly reducing exhaust backpressure and allowing the turbocharger to operate more efficiently. Ideal for Stage 2 builds and performance-focused vehicles.
⚠ IMPORTANT – EMISSIONS & ROAD USE NOTICE
This product removes the factory catalytic converter and is intended for off-road or motorsport use only. It is not UK road legal and will likely cause a UK MOT emissions failure. ECU tuning is required after installation.
Key Features＋
- Oversized 4.5″ Diameter: Significantly improves exhaust gas flow.
- High-Flow Decat Design: Eliminates restrictive factory catalytic converter.
- Stainless Steel Construction: Durable and heat-resistant.
- Mandrel-Bent Tubing: Smooth internal surface for optimal flow.
- Improved Turbo Response: Reduced backpressure improves spool.
- Aggressive Exhaust Tone: Enhanced turbo sound and exhaust character.
Why Upgrade Your B58 Downpipe?＋
- The factory catalytic converter is a major exhaust restriction.
- Reduced backpressure allows the turbo to operate more efficiently.
- Essential upgrade for Stage 2 ECU tuning.
- Improves throttle response and overall engine efficiency.
- Complements intake, intercooler and charge pipe upgrades.
Technical Specifications＋
- Material: 304 Stainless Steel
- Diameter: 4.5″ high-flow tubing
- Configuration: Decat (no catalytic converter)
- Construction: Mandrel bent & welded
- Fitment: Direct replacement downpipe
Vehicle Compatibility＋
- BMW M140i – B58 Gen 1
- BMW M240i – B58 Gen 1
- BMW M340i – B58 Gen 1
- BMW M440i – B58 Gen 1
✔ B58 Gen 1 engine only
✔ ECU tuning recommended
✔ Off-road or motorsport use only
Installation＋
- Remove factory catalytic downpipe.
- Install HFE decat downpipe using OEM mounting points.
- Check alignment and secure all connections.
- ECU remap required before driving.
- Professional installation recommended.
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