BMW x4 330D 2018

Service Completed: Cat-Back Exhaust System with Quad Exit Conversion

At MIJ Exhaust Ltd, we recently completed a custom cat-back exhaust upgrade on this 2018 BMW X4 30d xDrive 3.0L Diesel, transforming both the appearance and presence of the vehicle with a bespoke quad-exit exhaust conversion.

For this build, our experienced stainless steel exhaust fabricators manufactured and installed a custom cat-back exhaust system, replacing the mid and rear sections of the factory exhaust. The system was designed to enhance the vehicle’s rear-end aesthetics while maintaining excellent fitment and everyday usability.

One of the most noticeable aspects of this project was the quad-exit conversion. The BMW arrived at our workshop with the factory exhaust exiting from just one side of the vehicle. Following the upgrade, the exhaust now exits from both sides of the rear bumper, creating a far more balanced and performance-inspired appearance. This transformation gives the X4 a more aggressive and premium look that better suits the sporty character of BMW’s M Sport styling.

To achieve the conversion, we fabricated a bespoke rear section that distributes the exhaust flow evenly across both sides of the vehicle, resulting in a clean OEM+ finish and a symmetrical rear-end design. The quad-exit arrangement fills the rear valance perfectly and significantly enhances the vehicle’s road presence.

Alongside the visual upgrade, the custom cat-back system provides a deeper and more purposeful exhaust tone, giving the 3.0-litre diesel engine added character while remaining comfortable and refined for daily driving.

At MIJ Exhaust Ltd, we specialise in creating bespoke exhaust solutions that are tailored to each vehicle and customer. Whether it’s a subtle upgrade, a complete cat-back system, or a full rear-end conversion such as this, every system is fabricated in-house to ensure the highest standards of workmanship, durability, and fitment.

Be sure to check out the before image to see the original single-sided exhaust layout, and watch the accompanying sound test video to hear the upgraded exhaust note and see the completed quad-exit conversion in action.
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Why Choose a Custom MIJ Exhaust?

No two vehicles—and no two customers—are alike. That’s why every exhaust system we build is custom-made on the vehicle for the perfect fit, tone, and performance.

Whether you’re after:

A sportier, more aggressive sound,

A performance-focused setup, or

A refined, OEM-style tone,

—we tailor the design specifically to your goals.

More Than Just Custom Builds

We provide all types of exhaust services, including:

Exhaust repairs and leak fixes

Section replacements

Welding cracks and fault correction

Tailpipe upgrades and cosmetic enhancements

Small adjustments and one-off jobs