Stone Exhaust B58 Switchable Valved Cat-Back Performance Exhaust System (Catback) for BMW 3 Series G20/G21 M340i/M340i xDrive & 4 Series G22/G23/G26 M440i/M440i xDrive - OPF/GPF Compatible, Active Valve OEM Control, No Drone | AP546A

BMW B58 G20 G21 G22 G23 G26 Switchable Sports Exhaust - OPF and GPF Compatible - Stone AP546A

Give your 3 Series or 4 Series the soundtrack it should have. This Stone AP546A switchable sports system integrates with the factory flap motors on OPF and GPF cars, delivering a richer, deeper note when you want excitement and refined quiet when you do not. Designed specifically for the B58 platform on M340i and M440i models, it offers superb fitment, clean pipe routing and tangible performance benefits proven on Stone's in-house dyno.

If you are hunting for a BMW M340i or M440i upgrade that keeps factory drive modes intact while unlocking a motorsport-inspired tone with zero motorway boom, this is the plug-and-play solution that enthusiasts choose.

Why this system stands out

• Factory valve motor integration - uses the original actuators for seamless Comfort to Sport transitions.
• Precise OE-style fit - developed from detailed 3D scans for accurate alignment on OPF and GPF cars.
• Refined with valves closed, beefy and aggressive with valves open - without the annoying cabin resonance many systems suffer from.
• In-house development and dyno validation by Stone for real, repeatable gains and consistent quality.
• Optional Stone Valvetronic controller adds remote control and rpm-based auto open functionality via a simple OBDII plug-in.
• One-piece layout with precision machine welding for strength and lasting durability.

Valve control options

• Factory flap control: Retains ECU-managed valve operation. All standard drive modes work exactly as they should.
• Optional Stone Valvetronic (dual valves): Handheld remote to open or close at will, plus Auto Mode that opens at a chosen engine speed. Fast, plug-and-play OBDII install.

OPF and GPF friendly

Running a particulate filter. Stone provides an OPF solution that can be supplied free of charge, allowing trouble-free installation on filter-equipped cars without warning lights. No ECU coding required to suppress OPF messages.

Engineering detail

• 3D scanned development: OEM system mapped for optimised routing, diameters and bends.
• 7-axis CNC bending: Up to 98 percent roundness at tight 180 degree bends to protect flow and strength.
• Ultra-precise fabrication: Integrally moulded pipework with sub-0.025 mm accuracy helps minimise turbulence.
• Advanced weld techniques: Crisscross and overlapping welds at stress points with direct spot welding for accuracy and durability.

Vehicle coverage

Engine: BMW B58

BMW 3 Series

• G20 M340i and M340i xDrive (2018-2020)
• G21 M340i xDrive (2018-2020)

BMW 4 Series

• G22 M440i and M440i xDrive (2020+)
• G23 M440i xDrive (2020+)
• G26 M440i xDrive (2020+)

Part number

AP546A

Warranty

Stone Exhaust 2-year warranty.

Installation and fitting

This is a direct-fit system designed to work with the original valve motors. For a professional install, book with MJ Modifications in Warwickshire. Request a fitting quote at info@mjmodifications.co.uk.

Real-world feedback

We run Stone systems on our own B58 cars and have fitted them for many customers. The verdict is consistent: perfect OE-style fitment, a tasteful tone with the valves shut, a strong, sporty soundtrack with the valves open and no drone on long journeys.

Common searches for this upgrade

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