Switchable sports system for BMW F15 X5 35i and F16 X6 35i - Stone Exhaust valve-controlled cat back - AP522 and AP522Q
Give your 3.0 turbo straight six the sound and response it deserves. This Stone Exhaust valve-controlled cat back is engineered for the BMW F15 X5 35i and F16 X6 35i with the N55 engine, delivering a deeper tone, sharper throttle feel and factory-level fit without unwanted cabin resonance. Designed via 3D scanning, reverse engineering and validated on the dyno, it integrates with the car’s factory exhaust flap control for true OEM behaviour with a far more characterful soundtrack.
We have fitted multiple systems at MJ Modifications in Warwickshire and customer feedback has been consistently excellent. Fitment is precise, valve operation is seamless and the sound is refined with the valve closed yet properly sporty when opened. If you want an active exhaust upgrade for your X5 35i or X6 35i that looks right, fits right and sounds right, this is the one.
Key reasons to choose this upgrade
- Factory valve integration - the ECU manages the flap just like stock for effortless day-to-day use
- Optional remote control - add Stone’s Valvetronic single-valve kit with plug-and-play OBD controller for on-demand sound
- Proven on the dyno - developed for improved gas flow and response while maintaining liveable NVH
- CNC precision - 7-axis bending, high roundness and tight tolerances for smooth flow and spot-on alignment
- Robust construction - one-piece sections, overlapping and crisscross welding, mechanically assisted spot welds
- Minimal drone - designed to reduce cabin boom common on many aftermarket systems
- Direct bolt-on - 3D scanned for 100 percent compatibility with F15 X5 35i and F16 X6 35i platforms
- Tailpipe choice - twin exit or quad exit options to suit your bumper setup
Part numbers
- AP522 - Dual exit with twin tailpipes. Requires the original bumper.
- AP522Q - Dual exit with quad tailpipes. Requires X6M bumper.
Compatibility - N55 3.0 petrol turbo
- BMW F15 X5 35i - 2013 to 2018 - including xDrive 35i
- BMW F16 X6 35i - 2013 to 2018 - including xDrive 35i
What it sounds like
F16 X6 35i with Stone Eddy high-flow catted downpipe and factory rear section
F16 X6 35i with Stone Eddy high-flow catted downpipe and Valvetronic cat back
Installed photos
Engineering detail
Stone’s process starts with laser 3D scanning and a full reverse engineering study of the OE path to optimise tube diameter, routing and bend radii. Computational analysis is then used to model flow, backpressure and thermal behaviour before a single tube is bent.
Manufacturing is completed on a 7-axis CNC bending cell to maintain up to 98 percent roundness through tight radii, minimising outer wall thinning and flow disturbance. Tolerances are held to approximately 0.025 mm for a precise, repeatable fit. High-heat zones receive overlapping and crisscross welds and mechanically assisted direct spot welds for strength and longevity.
Fitting and support
Professional fitting available at MJ Modifications in Warwickshire. For a fitting quote, valve control advice or to book workshop time, email info@mjmodifications.co.uk.
Warranty
Stone Exhaust 2-year warranty.
Manufactured by
Stone Exhaust
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