1 1

Stone Exhaust

Stone Exhaust BMW 320i/420i (B48) Valved Cat-Back Exhaust System – F30 F31 F32 F33 F36 (incl. xDrive) | OEM Integrated Valve | Single/Dual/Quad Exit Options

Stone Exhaust BMW 320i/420i (B48) Valved Cat-Back Exhaust System – F30 F31 F32 F33 F36 (incl. xDrive) | OEM Integrated Valve | Single/Dual/Quad Exit Options

£2,396.16
£2,995.20 £2,396.16
Sale Sold out
Shipping calculated at checkout.
Exhaust Style
Tailpipe Finish

Heads-up on cancellations & returns: if you cancel an order or return an item, you won't get back 100% of what you paid. We apply a 10% restocking fee, the outbound shipping is non-refundable, and we have to pass on Shopify / PayPal payment processing fees; these aren't returned to us when we refund you. International orders also lose on exchange-rate spread in both directions. If the original packaging is damaged or missing, a reboxing charge applies. For international orders specifically, if you refuse to pay our shipping invoice or supply a prepaid label after placing the order, the same deductions apply. We're upfront about this — please be sure of your purchase before ordering.

Stone Exhaust switchable catback for BMW 320i and 420i B48 - F30 F31 F32 F33 F36 including xDrive

Transform the character of your two-litre turbo BMW with the Stone Exhaust valve-controlled catback. This premium rear system unleashes a richer tone, sharper throttle response and improved flow, while keeping everyday refinement intact when the flap is shut. Designed using full 3D scanning of the factory hardware and validated on Stone’s in-house dyno, it delivers precise, direct-fit installation and a deep, refined soundtrack without cabin drone.

We have installed and used this system ourselves at MJ Modifications and customer feedback on sound quality, craftsmanship and perfect fit has been superb. If you want a subtle commute yet an exciting soundtrack on demand, this is the upgrade to choose for your B48-powered 3 Series or 4 Series.

What you will love

  • Factory valve integration for OEM-style control through your car’s ECU
  • Optional Stone Valvetronic add-on for remote open or close via an OBDII plug-and-play controller
  • One-piece layout for optimal gas flow and straightforward fitment
  • No unwanted resonance in the cabin - refined on cruise, purposeful under load
  • Engineered from 3D scans for true direct-fit installation on B48 models
  • Dyno-developed by Stone Exhaust for genuine performance benefits
  • Built with precision crisscross and overlapping welds for strength and longevity

Valve control options

OEM integrated valve control - works like standard. The ECU operates the flap automatically, giving a calm drive at light throttle and a sportier tone when you ask for it.

Optional Valvetronic controller - add a single valve remote control with a simple OBDII plug-in module so you can choose quiet or loud at the press of a button.

Vehicle compatibility - B48 models

3 Series

  • F30 320i and 320i xDrive 2011+
  • F30 LCI 320i and 320i xDrive 2014+
  • F31 320i 2011+ and 320i xDrive 2012+
  • F31 LCI 320i and 320i xDrive 2014+

4 Series

  • F32 420i and 420i xDrive 2013+
  • F32 LCI 420i and 420i xDrive 2016+
  • F33 420i 2013+ and F33 LCI 2016+
  • F36 420i and 420i xDrive 2013+
  • F36 LCI 420i and 420i xDrive 2016+

Tailpipe layouts and part numbers

  • AP502B48 - Single exit with left twin tips - uses the original bumper
  • AP502NB48 - Dual exit with twin tips - requires 340i or 440i rear bumper
  • AP502NQB48-8200CG - Dual exit with quad tips - requires M Sport rear bumper

Hear it

Dyno developed

Stone Exhaust dyno development for BMW B48 catback

Installed examples

Stone Exhaust fitted - dual exit layout
Stone Exhaust installed - B48 platform

Engineering detail that sets it apart

R and D with 3D scanning
Stone maps the factory system to optimise tube diameters, routing and bend geometry for the B48 platform. Computational analysis of gas speed, pressure and temperature helps achieve the best blend of tone and flow while ensuring exact fitment.

3D scanning and reverse engineering by Stone Exhaust

7 axis CNC bending
Precision mandrel bends maintain roundness and minimise deformation at tight angles, cutting restriction and keeping welds stress free. With reverse engineering and CNC-controlled forming, tolerances are exceptionally tight for a true direct fit.

Stone Exhaust 7 axis CNC bending quality

Advanced welding techniques
Crisscross and overlapping welds reinforce high heat areas for long-term durability, while mechanical spot welding ensures consistency and a premium finish.

Stone Exhaust welding quality - detail 1
Stone Exhaust welding quality - detail 2

Warranty

Stone Exhaust 2-year warranty.

Professional fitting

For supply and installation, choose MJ Modifications in Warwickshire. We offer expert fitting and bumper conversion advice for twin or quad layouts. Request a quote at info@mjmodifications.co.uk.

Helpful search terms

BMW 320i sports exhaust, BMW 420i sports exhaust, F30 F31 F32 F33 F36 switchable exhaust, B48 turbo catback, BMW flap exhaust, BMW ECU valve exhaust, BMW 3 Series performance rear system, BMW 4 Series performance rear section, BMW xDrive compatible exhaust, BMW twin tip upgrade, quad tip upgrade, dual exit rear conversion, direct fit exhaust for BMW B48, plug-in OBD valve controller, back box upgrade, BMW 320i sound upgrade, BMW 420i sound upgrade, Stone Exhaust UK dealer, no drone BMW exhaust, performance exhaust for 2.0 turbo BMW.

View full details