B46/B48 Downpipe Install

Factory close-coupled catalytic converter at the turbo outlet (what most owners call the downpipe). Renew turbo joint seals and clamps, swap the converter if needed, torque every joint per the table.

When you are doing this job

Leaks at the turbo V-band or V-clip, rattling from a loose joint, or a converter that failed internally. This guide covers factory BMW parts only: gasket ring, clamps, and the correct close-coupled catalytic converter for your VIN.
Not a shortcut around emissions hardware. We do not cover test pipes, deletes, or non-factory converters.

G20 330e and similar PHEV: BMW's repair text starts with high-voltage danger and hybrid-trained personnel only. If that is your car, stop and use the PHEV procedure.

Which cars (US)

B46 and B48 engines in BMW and MINI sold here, including F22/F23 230i, F30/F31/F34 330i, F32/F33/F36 430i, G20 330i, G30 530i and 530e, G01 X3, G02 X4, G29 Z4, F48 X1, F39 X2, F44 2 Series Gran Coupe, 330e, 740e, and MINI with B46/B48. Close-coupled converter number, second-joint clamp diameter, and turbo joint torque differ by model: send us your VIN and we will send yours.

Parts by car

Turbo joint setGasket 18 30 7 581 970 + V-band 18 30 7 606 136Fits most B46/B48 turbo outlets in the catalog.

Turbo joint kit →$60.99

Second joint clamp, 80.0 mm18305A09B63 (replaces 18 30 8 631 986)G20, F3x, G30, G01, G02, G29, and many lengthwise F-chassis cars.

Full set 80.0 mm →$117.99

Second joint clamp, 70.0 mm18305A04BD6 (replaces 18 30 8 616 159)F48 X1, F39 X2, F44, and most MINI B46/B48 on the US catalog diagrams we checked.

Full set 70.0 mm →$115.99

Second joint clamp, 72.0 mm18 30 8 632 362F57 JCW B48 on one MINI diagram. Send us your VIN and we will send yours if you are unsure.

330e / 740e rear joint18 30 8 623 284F30N 330e and G12 740e use this muffler clamp at the cat. Those PHEV layouts have no separate second clamp like the 80.0 mm joint.

Close-coupled cat, G20 330i / G30 530i / Z4Examples: 18 32 8 482 648, 18 32 9 452 475, 18 32 8 659 799Converter assembly is VIN and emissions spec. F-chassis, X models, and MINI use their own numbers such as 18 32 8 685 968 or 18 32 7 634 634. Send us your VIN and we will send yours.

Holder near transmission18 32 8 642 576 or 18 32 8 659 800G20/F3x/G01/G02/G29 families. Hardware kit 18 30 7 620 661 on many F-chassis and G01 cars.

How the converter comes out (by model)

G20 / G30 / G01 / G02 / F3x (lengthwise)After the exhaust is lowered, release the turbo V-clip and guide the converter out in the direction BMW marks with an arrow. Version B cars also disconnect the PPF pressure hose at the cat.

F39 X2 (top feed)More under-hood work: cowl, bulkhead, intake silencer, strut brace, and clean-air pipe off first, then heat shields until you can feed the converter out upward past the turbo area.

G29 Z4 (bottom pull)Battery earth leads off, underbody and stiffening plate off, full exhaust dropped, then pull the converter out toward the bottom of the car.

Out in this order (G20 330i path)

What comes off before the converter moves

Cool exhaust onlyhot pipes burn
Rear bonnet seal and acoustic coversroom at the turbo
Front O2 sensor wiring and sensorSW 22, black cable
Positive battery cable routed asideshort-circuit risk
Tunnel connecting supportsee torque table
Rear torsion struts and Y-strutjoining torques + 90°
Complete exhaust loweredhelper + jack

Drawing of the converter holder and hanger bolts under the car with numbered dots: 1 Converter holder bolts (crow's-foot spot) — Figure 1The converter holder bolts at the hanger, where a crow's-foot earns its keep

Figure 1The converter holder bolts at the hanger, where a crow's-foot earns its keep

Centre underbody protection
Turbo V-clip releasednew clip on install; Version B: PPF hose off

Drawing of the turbo joint set: V-band clamp and gasket ring with numbered dots: 1 Turbo V-band clamp (renew); 2 Turbo gasket ring (renew) — Figure 2The turbo joint set: new V-band clamp and new gasket ring, both renewed every time

Figure 2The turbo joint set: new V-band clamp and new gasket ring, both renewed every time

Close-coupled catalytic converternew seal, new clips/clamps; clear monitoring O2

F39 X2 and Z4: different upfront teardown (above), same turbo joint parts. Legacy xDrive top-feed: propeller shaft and more underbody work, cat out upward.

Drawing of the close-coupled catalytic converter seen from under the car on a lift with numbered dots: 1 Close-coupled catalytic converter (downpipe); 2 Monitoring O2 sensor cable; 3 Underbody panel (comes off first) — Figure 3Under the car on a lift: the close-coupled converter, its O2 cable, and the underbody panel that comes off first

Figure 3Under the car on a lift: the close-coupled converter, its O2 cable, and the underbody panel that comes off first

Tools

O2 sensor socket SW 22 and BMW tool S 117 020 if you have it. A crow's-foot on an extension helps the front O2 and the hanger-area converter bolts in tight spaces.
Sockets and wrenches for M6 to M12 exhaust hardware, Torx and hex as your car uses, plus a torque wrench that reads from 2.6 Nm up.
Jack and stand to support the exhaust and catalytic converter. BMW expects a second person for the heavy sections.
Distilled water only if you reinstall acoustic covers below 20 degrees C: BMW forbids lubricants on those seals.

Safety and support

Work on cooled exhaust only. Support the exhaust and converter on a jack and secure them so they cannot fall. Do not pull on O2 sensor wires at the connectors. Protect the monitoring O2 sensor during removal and install.

Do not drive without the tunnel connecting support, torsion struts, or (on Z4) the stiffening plate reinstalled and torqued.

Route the positive battery cable without abrasion or trapping. After the exhaust is back together, check the system for leaks before road use. On Z4, disconnect all battery earth leads before work.

Torque (by joint)

Turbo V-band clamp (B48 torque table)32 Nm

Turbo V-clip, G20 / G20 PHEV repair text13 Nm

Turbo V-band / V-clip, Z4 and F39 X2 repair text13 Nm

Converter to holder, M8 (G20 install)19 Nm

Holder on transmission (B48 table)66 Nm

Exhaust to converter, flat band clip (B48 table)28 Nm

Exhaust to converter, G20 ribbon clamp M8 nut26 Nm

Exhaust to converter, G20 ribbon clamp M10 nut55 Nm

Rear V-clip, G20 Version B25 Nm

Exhaust to converter, Z4 clamp (no PPF)26 Nm

V-clip to cat, Z4 with PPF rear joint25 Nm

Front O2 sensor M18x1.550 Nm

Monitoring O2 sensor M18x1.550 Nm

Rear silencer to body, M819 Nm

Connecting support to tunnel, M8x2520 Nm

Connecting support to compression strut, M10x3056 Nm

Y-strut to adapter (joining torque)56 Nm + 90°

Torsion strut to mount (joining torque)100 Nm + 90°

Torsion strut to compression strut, M828 Nm

Torsion strut to body, M612 Nm

Heat insulation to connecting support2.6 Nm

Underbody protection panel bolt3 Nm

PPF pressure line nut at cat (F39)20 Nm

Turbo joint tightening torque on your carSend us your VIN and we will send yours.

Steps (G20 path)

Work through the removal map above to the converter. Do not hang weight on O2 wiring; protect the monitoring O2 on the way out.
Move the monitoring O2 to the new converter and tighten to 50 Nm with light even thread grease, not on the ceramics.
Install the new converter with new V-clips and seal; torque the turbo V-clip to 13 Nm and holder fasteners to 19 Nm with new M8 hardware as required.
Figure 4Generic layout: gasket ring at the turbo flange, V-band clamp, holder bracket
Figure 4Close
Reinstall the exhaust from rear to front with new ribbon clamps and hanger nuts; torque joints per the table. Car voltage-free.
Reinstall tunnel support, underbody, front O2, battery cable routing, and acoustic covers.
Check exhaust tightness.

ZF 8HP automatic: fluid and pan (Part 2)

Under the car: GA8HP50Z ATF and pan on lengthwise B46/B48 automatics in the US list above (F2x, F3x, G20, G30, G01, G02, G29). F48 X1, F39 X2, F44, and MINI use front-drive GA6F21AW: Part 2 does not apply. F30N 330e and G12 740e use GA8P75HZ with high-voltage rules and a different pan: not the kit below. Planning an engine tune and a transmission tune after the downpipe? Do this service first: more torque through old fluid is what wears the clutches, seals, and mechatronic.

Our ZF 8HP service kit24 11 86 129 01Pan with integrated filter, 7 L ZF ATF, and 13 bolts for GA8HP50Z service on lengthwise cars above.

ZF 8HP service kit →$386.99

8HP tools and setup

Scan tool with BMW diagnosis to read transmission oil temperature and run the Transmission control unit oil adjustment service function after refill.
ATF filler plug tool 24 05 614 for the setpoint torque on the filler plug.
Drain pan, gloves, and ventilation for ATF contact and vapours. Vehicle horizontal, selector in P, parking brake on (ZF service note).

Level is temperature-based. BMW sets ATF level with oil at 30 to 40 degrees C at the start of the adjustment and 40 to 50 degrees C when you finish. Read oil temperature with your scan tool; guessing the level is how transmissions get ruined. ZF notes incorrect level low or high can damage the unit or overflow when hot.

After any pan service, skipping the diagnosis oil level adjustment can cause serious automatic transmission damage. Renew the oil filler plug and sealing ring every time.

8HP torque

ATF drain plug, plastic sump8 Nm

ATF filler plug (with tool 24 05 614)35 Nm

Sump to transmission, aluminium pan screws (step 1)4 Nm

Sump aluminium screws (step 2 angle)45 degrees

Sump to transmission, steel pan screws10 Nm

Pan bolt type on your sumpSend us your VIN and we will send yours.

8HP steps (GA8HP50Z)

Drain ATF from the drain plug, then remove the transmission oil pan per BMW pan service procedure for your chassis. Gloves, BMW-approved ATF, and the scan tool ready first.
Figure 5ZF 8HP pan with integrated filter and the ATF drain plug
Figure 5Close
Install a new pan with integrated filter and new pan screws; torque aluminium screws to 4 Nm plus 45 degrees, or steel screws to 10 Nm, per your sump type.
Figure 6Pan off: the mechatronic sits right there, so keep your hands off its contacts
Figure 6Close
Refill ATF on a level surface with the car secured against rolling; run Transmission control unit oil adjustment with oil at 30 to 40 degrees C at start and 40 to 50 degrees C at finish.
Install a new oil filler plug and sealing ring; tighten the filler plug to 35 Nm with tool 24 05 614.
Reinstall the drain plug to 8 Nm on a plastic sump.
Check for leaks.

330e / 740e: different hybrid transmission and pan, high-voltage rules, not this kit: send your VIN.

Where people mess it up

Reusing the turbo V-band, V-clip, flat band clip, or gasket ring. BMW treats them as one-time at this job.
Letting the exhaust or converter hang on the O2 sensor or wiring. Disconnect and support the weight.
Wrong turbo torque spec. G20 repair text and the B48 torque table do not always match: send us your VIN and we will send yours.
Ordering the 80.0 mm second clamp for an X1, X2, or MINI that needs 70.0 mm. Measure or confirm by VIN.
Setting ATF level without the scan tool temperature window or skipping oil adjustment after a pan job.
Reusing sump screws, filler plug, or sealing ring on GA8HP50Z or GA8P75HZ pans. BMW calls for new hardware.

Shop tip:

The lower clamp is only for the rest of the exhaust; the upper clamp at the turbo is the main big one. Always replace both when you are in there.

Shop tip:

On a lift, expect a lot of top and bottom maneuvering on the converter. A crow's-foot on an extension makes the oxygen sensors and the hanger-area downpipe bolts much easier.

Shop tip:

Making real power with the downpipe takes a custom engine tune and a custom ZF8 transmission tune. An off-the-shelf stage 3 ZF8 tune works, but it can't keep up, and you'll have to warm the transmission up for a long time before every hard drive. Street cars: run a catted converter with a CARB EO number.

Shop tip:

On lengthwise automatics, skip the ZF 8HP service and the driveline pays: diffs, seals, and the mechatronic. See our ZF 8HP service kit for F2x, F3x, G20, G30, G01, G02, and G29. F48 X1, F39 X2, F44, and MINI use a different automatic: not that kit. ZF notes ATF ages faster with high heat, lots of high speed driving, towing, and sporty driving.

Steps, torque values and part rules come from BMW's repair instructions for the close-coupled catalytic converter and GA8HP50Z automatic oil service on B46/B48 cars. Part numbers come from BMW's parts catalog up to 2020. Check yours by VIN. ZF level guidance is paraphrased from ZF aftermarket service information, with owner shop tips labeled.