This installation guide explains how to remove the factory catalytic converter and install a downpipe on BMW G20/G21 models equipped with the B48 engine, including the 320i, 330i, and 330e.

Installation Information:

Vehicle platform: BMW G20 / G21
Engine: B48
Models: BMW 320i / 330i / 330e
Estimated installation time: 1.5 hours
Installation difficulty: Intermediate
Installation location: Engine bay + underneath the vehicle

Before You Start:

Before beginning the installation, allow the exhaust system to cool completely.
Support the vehicle securely and follow the vehicle manufacturer's workshop procedures for lifting, access, and component removal.
Wear suitable eye and hand protection when working with or handling exhaust components.
Make sure you have all required tools and replacement hardware available before starting the installation.

Removing the BMW B48 Factory Catalytic Converter

1. Disconnect the Lambda Sensors and OPF Hose

We recommend starting the removal of the factory catalytic converter from the engine bay, while the vehicle is still on the ground and has not yet been raised on a lift.
First, remove the plastic engine cover. You will then have easy access to the connectors for the two lambda (O2) sensors. Disconnect both sensor connectors.

bmw b48 connectors for the two lambda (O2) sensors

You will also need to disconnect the small hose connected to the OPF sensor.

2. Loosen the Turbocharger Clamp

There is enough space around the turbocharger to access and loosen the clamp connecting the factory catalytic converter to the turbocharger.
Once these components have been disconnected, raise the vehicle and continue the installation from underneath.

Loosen the Turbocharger Clamp bmw b48 330i

3. Raise the Vehicle and Remove Underbody Protection

Before starting work underneath the vehicle, we recommend creating as much working space as possible by removing any protective shields or underbody panels that may be in the way.

4. Disconnect the Factory Catalytic Converter from the Midpipe

Next, remove the bolt securing the midpipe. Then loosen and disconnect the clamp connecting the catalytic converter to the midpipe.

Disconnect the Factory Catalytic Converter from the Midpipe bmw b48 330i

In many cases, the original midpipe clamp cannot be reused after removal. For this reason, we recommend installing a new clamp (BMW Genuine B48 Clamp: 18-30-5-A09-B63). A replacement clamp can be ordered together with the downpipe. Check out AXI BMW 320i / 330i / 330e G20/G21 B48 Downpipe with BMW Genuine Clamps & Gasket

5. Remove the Factory Catalytic Converter from the Mounting Bracket

Once the catalytic converter has been separated from the midpipe, disconnect it from its mounting bracket by removing the two retaining bolts.The factory catalytic converter can now be removed relatively easily from underneath the vehicle.

6. Remove and Transfer the Lambda Sensors

Before installing the new downpipe, remove the two lambda sensors from the factory catalytic converter. Transfer both sensors to the new downpipe and reconnect the OPF hose.

Installing the BMW B48 Downpipe

1. Connect the Downpipe to the Turbocharger

Installation of the downpipe is carried out in the reverse order of removal.
Start by connecting the downpipe to the turbocharger. At this stage, do not fully tighten the turbocharger clamp.
We recommend using a new BMW Genuine B48 Turbo Clamp: 18-30-7-606-136 together with a new BMW Genuine B48 Turbo Gasket: 18-30-7-581-970 to ensure a proper and reliable seal. You can order our BMW G20/G21 B48 downpipe together with a set of OEM BMW clamps and a turbo gasket.

2. Reconnect the Lambda Sensors and OPF Hose

Next, reconnect the wiring connectors for both lambda sensors and reconnect the OPF sensor hose.

3. Secure the Downpipe to the Mounting Bracket

Working underneath the vehicle, secure the downpipe to the factory mounting bracket using the two retaining bolts.

4. Connect the Downpipe to the Midpipe

Then connect the downpipe to the midpipe using the new BMW Genuine B48 Clamp: 18-30-5-A09-B63.

5. Check Alignment and Tighten All Connections

Before fully tightening all connections, check that the downpipe is correctly positioned and that there is sufficient clearance from surrounding components.

6. Reinstall the Underbody Protection

Finally, reinstall any protective shields, underbody panels, and plastic components that were removed during the installation process.

After completing the installation, perform a final inspection of all connections, clamps, sensor wiring, and the OPF hose before starting the vehicle!

Ready to upgrade your G20/G21 B48 exhaust system? View our BMW G20/G21 B48 downpipe and OPF delete pipe for 320i, 330i and 330e models: