B58 Racing

Buying guide · Gleb Blekher

B58 Downpipe Install Guide: Gen 1 F-Chassis, Gen 2 G-Chassis and the GR Supra

Short answer: A B58 downpipe swap is a bolt-on job. You undo one V-band clamp at the turbo, the joint at the mid pipe and a support bracket, move the two oxygen sensors over, and fit the new pipe with a fresh turbo gasket. Plan on 2 to 4 hours on jack stands, less on a lift, and more on an xDrive car. The hard parts are reaching the front O2 sensor, seating the pipe square on the turbo and lining it up with the rest of the exhaust before anything gets tightened. Then load a tune that supports the pipe before you drive it hard.

Parts and tunes in this guide are for off-road / competition use only. Not legal for use on public roads in the United States, including California.

I'm Gleb Blekher. I run B58 Racing out of Dallas, TX. Both of my B58 cars run a downpipe, and it's the part we get the most install questions about. This guide pulls together what the downpipe makers publish in their own instructions, plus what owners report on the forums. Where the sources don't agree, or don't say, I'll tell you.

Who this guide is for

This covers the factory-turbo B58 in three families:

FamilyCarsEngineNotes
Gen 1 F-chassisM140i (F20), M240i (F22/F23), 340i (F30), 440i (F32/F33/F36)B58B30M0RWD and xDrive
Gen 2 G-chassisM340i (G20), M440i (G22/G23/G26), M240i (G42), Z4 M40i (G29)B58TU2019–2024 cars; xDrive on most 3/4 Series
GR Supra 3.0A90/A91B58TURWD only

Not sure which engine you have? Read our B58 Gen 1 vs Gen 2 guide first. The 540i, 740i and X3 M40i also use the B58, but their downpipes and brackets differ, so check the listing for your exact car.

2025 and newer M340i/M440i (B58N) owners: stop here. Active Autowerke says the factory downpipe on these cars carries a particulate filter and that removing it takes 9 to 10 hours because the subframe has to come down. That's a shop job, and it's not the procedure below.

Difficulty, time and whether you need a lift

  • Difficulty: 3 out of 5. No cutting, no welding, but tight access and a heavy, awkward pipe.
  • Time: 2 to 4 hours on jack stands. One retailer quotes 2 to 4 hours DIY and about half that on a lift. Scorpion's fitting sheets estimate 1 to 1.5 hours, which is a pro-on-a-lift number. A G42 M240i owner on Bimmerpost rated the job 2 out of 5 but said it is not an easy 1 to 2 hours without a lift and a helper. Another owner reported doing an M340i xDrive alone, on ramps, in a little over an hour. Your first time will take longer than either.
  • Lift: not required. AMS says its Supra downpipe can go in entirely from underneath. Good jack stands on a level floor are the minimum. A helper makes lining up the pipe much easier.
  • xDrive: add time. The front driveshaft sits next to the downpipe and crowds your hands and the pipe on the way out. We could not find a manufacturer procedure with extra xDrive steps, and many downpipes (for example CTS Turbo's) are sold as one part for RWD and xDrive. Expect less room, not a different job.

Tools

These are the sizes the brands list in their own instructions. Your car may differ by year, so have a full metric set on hand.

  • 13 mm socket and wrench. CTS (F30 340i), AMS and MAP (Supra) all use 13 mm for the V-band clamp, hanger nuts, bracket nuts and the clamp at the mid pipe.
  • 8 mm socket for the plastic undertray screws (CTS, F30).
  • T50 Torx for the underbody support brace on the F30 (CTS).
  • 22 mm O2 sensor socket. AMS lists a standard 22 mm O2 socket. MAP lists a 22 mm combination wrench.
  • Long flex-head wrench or ratchet. AMS says you'll need one to reach the front O2 sensor from underneath on the Supra.
  • Pick tool for the O2 sensor connector tabs.
  • Flat screwdriver and a small pry bar for stuck V-bands and the intake clamp.
  • Jack and jack stands (or a lift), plus a second jack or stand to hold the exhaust.
  • Torque wrench, penetrating oil, gloves and eye protection.
  • High-temperature anti-seize for the O2 sensor threads, unless your new sensors or pipe say otherwise.

Parts list

You need the downpipe, a new turbo-to-downpipe gasket, and a tune that supports the pipe. Every link below fits the cars named next to it.

Turbo gasket. BMW part 18328612538 (Toyota 17279-WAA02 on the Supra). CTS doesn't include it and recommends buying it from a BMW dealer. Active Autowerke pre-installs a gasket in the flange of its downpipes. AMS says you can reuse the original if most of the sealing face is intact. We'd buy a new one. It's cheap and it's the most common source of leaks.

Gen 1 F-chassis (M140i, M240i, 340i, 440i):

Gen 2 G-chassis (M340i, M440i, M240i, Z4 M40i):

Fits both Gen 1 and Gen 2 BMWs:

GR Supra 3.0 (A90/A91):

Race downpipes for track cars (Gen 1, Gen 2 and Supra): Spool's 4.5" race downpipe, 5" race downpipe and 5" 200-cell catted downpipe. Confirm your engine with us before ordering.

Browse everything in B58 downpipes.

Step-by-step: B58 downpipe install

The order below follows the CTS Turbo guide (shot on a 2016 340i), the AMS and MAP guides (GR Supra) and the Scorpion fitting sheets. Gen 2 BMWs follow the same pattern: V-band at the turbo, a bracket, and a joint at the mid pipe. We could not find a brand's step-by-step written for the G20, G22 or G42 specifically, so read the sheet that comes with your pipe and follow it where it differs.

Stage 1: prep

  1. Let the car cool completely. The turbo and downpipe are the hottest parts of the car. CTS and AMS both say not to start until it's cold.
  2. Soak the hardware the night before. Spray the V-band nut, the mid-pipe clamp or bolts, the hanger nuts and both O2 sensors with penetrating oil.
  3. Raise the car and support it on jack stands on a level surface. Never work under a car held only by a jack.
  4. Remove the underbody covers. On the F30, CTS removes the plastic undertray (8 mm screws) and the metal tray (13 mm).
  5. Remove the engine cover and airbox (optional but helpful). CTS pulls the airbox on the 340i to reach the O2 connectors. On the Supra, AMS lists airbox removal as optional and MAP removes the cover and intake.

Stage 2: removal

  1. Unplug the O2 sensor connectors. They're clipped to a bracket on the engine. Use a pick to release the locking tab and slide each connector off the bracket. CTS says they slide toward the front of the car on the 340i. MAP says on the Supra you move the tab toward the back of the car and slide the connector toward the valve cover. Look before you pull.
  2. Loosen the V-band clamp at the turbo (13 mm). CTS warns not to back the nut off too far, because there's a nut on the other end of the T-bolt. If the clamp sticks to the flange, AMS pries it free from the right side and through the hole in the motor mount bracket.
  3. Remove the downpipe bracket nuts (13 mm). CTS removes two 13 mm nuts from the hanger on the 340i. AMS and MAP remove two 13 mm nuts from the downpipe support bracket on the Supra. AMS notes a clip on the bracket mount that has to be held open.
  4. Support the exhaust, then free the back of the downpipe. On the F30, CTS removes the support brace under the car with a T50 Torx, puts a stand under the exhaust and removes the two 13 mm bolts at the bottom of the downpipe. On the Supra, the downpipe slips into the exhaust. Loosen the 13 mm clamp nut and remove the front exhaust hanger nut so the exhaust can hang. A twist helps it come free.
  5. Lower the downpipe out. MAP rotates the Supra pipe off the bracket studs. On an xDrive BMW, work it past the front driveshaft slowly rather than forcing it.

Stage 3: install

  1. Move the O2 sensors to the new pipe. Use the O2 socket. Transfer them one at a time so the upstream and downstream sensors go back into the correct bungs, as CTS and MAP both stress. If the new pipe doesn't come with anti-seize already on the threads, add a light coat to the threads only.
  2. Fit the turbo gasket. If your pipe has one pre-installed, leave it. If you're reusing or moving the factory gasket, AMS works it out of the old flange with a razor blade or small screwdriver. Check the turbo flange too, so you don't end up with half an old gasket stuck there and a new one on top.
  3. Hang the pipe loosely. AMS's order on the Supra: slide the V-band back off the flange, seat the outlet into the exhaust first, then put the bracket on its studs, and make sure the flange is fully seated on the turbine housing outlet. CTS's order on the 340i: install the gasket, then the V-band, then the hanger nuts, and don't fully tighten anything yet.
  4. Reconnect the exhaust. Refit the mid-pipe bolts or clamp and the hanger hardware, loose.
  5. Check alignment before torque. Look for contact with the subframe, steering shaft, starter and body. AMS sets about a 1/8" gap between its downpipe and the starter on the Supra.
  6. Tighten in order. AMS tightens the two bracket nuts first to hold the flange square, checks the flange is still seated, then fits and snugs the V-band, then loosens the bracket nuts so the pipe can settle, then does the final tightening. CTS just says to make sure everything is seated, then tighten the V-band, hanger, exhaust hanger and clamp. Torque to the value in the instructions supplied with your part. We could not find a published BMW torque for the B58 turbo V-band, and forum numbers we found are unconfirmed. Don't guess, and don't lean on it. An over-tightened V-band can leak or crack.
  7. Refit the O2 sensors and connectors. AMS's tip: pre-twist each sensor counterclockwise before threading it in, so the harness ends up straight when the sensor is tight. Route the wires away from the pipe and clip the connectors back into their brackets.
  8. Refit the braces, trays, airbox and engine cover. Make sure the airbox clips and intake sensor plug are locked.

Stage 4: after the install

  1. Leak check. Start the car cold and let it idle. Listen at the turbo flange for a tick or puff. On a cold car you can carefully feel for gas at the mid-pipe joint. Exhaust smell in the engine bay usually means a leak at the turbo, not normal.
  2. Scan for codes. Use an OBD-II scanner before and after the first drive. A loose O2 connector or a leak upstream of a sensor can set codes and skew the tune.
  3. Tune and coding. Your car needs a tune that supports the downpipe. Load it before any hard driving. On a stock map, a high-flow or race pipe can set a catalyst-efficiency code (P0420 is common), and you'll get little of the gain. Brands differ on catted pipes. Active Autowerke says its catted pipes need no performance tune. CTS says its high-flow cats need Stage 2 software or the check engine light will come on. Fabspeed claims no check engine light. Follow your pipe maker and your tuner.
  4. Recheck after a few heat cycles. Retighten clamps and hanger hardware to spec once the car has been through a few full heat cycles.

Gen 1 vs Gen 2 vs Supra: what actually changes

  • Gen 1 F-chassis. The CTS steps above were shot on this car. Expect the T50 support brace under the car and a bolted joint at the bottom of the downpipe.
  • Gen 2 G-chassis. Same idea, but no brand we found publishes G20-specific steps. Owners report the job is fine on ramps or stands with patience. Check your build date: 2025+ B58N cars are a different, much bigger job.
  • GR Supra. RWD only, slip-fit joint at the cat-back with a 13 mm clamp, and a two-stud bracket with a retaining clip. The front O2 sensor is the hardest part to reach from underneath.
  • xDrive (BMW only). Less room around the front driveshaft. Budget extra time and consider a lift.

Common mistakes and how to avoid them

  • Double gasket or no gasket. A SupraMKV owner chasing exhaust smell after an install was told to check for exactly this: part of the old gasket left on the turbo with a new one on top. Clean the turbo flange and use one gasket.
  • V-band clocked wrong or not seated. If the flange isn't fully on the turbine outlet, the clamp will feel tight and still leak. AMS verifies the flange visually through the motor mount bracket before and after tightening the bracket. Point the clamp's T-bolt where you can reach it later. AMS angles it for access from above.
  • Over-tightening the V-band. More torque doesn't seal a misaligned flange. Fix the alignment, then torque to your part's spec.
  • Tightening the turbo end first. That locks the pipe in a bad position and loads the flex section and bracket. Hang everything loose, line it up, then tighten in order.
  • O2 sensors swapped or wires twisted. Move them one at a time. Pre-twist before threading. Keep wires off the pipe.
  • Heat shields left loose or forgotten. Refit every shield and tray you removed. A loose shield rattles and looks like a bigger problem than it is.
  • Wastegate rattle. A louder downpipe can make an existing turbo or heat-shield rattle easier to hear. Check shields and hardware first. A downpipe install doesn't adjust the wastegate.
  • Driving on a stock map. Expect codes and possible boost cuts. Have your tune ready before the car comes off the stands.
  • Mixing up generations. Read the listing for your engine and build date. Several pipes cover Gen 1 and Gen 2. Others don't.

FAQ

How long does a B58 downpipe install take?

About 2 to 4 hours for most DIYers on jack stands, and less on a lift. Brand fitting sheets quote 1 to 1.5 hours, which assumes a lift and experience. xDrive cars take longer because the front driveshaft limits room.

Can I install a B58 downpipe without a lift?

Yes. AMS says its Supra downpipe can be installed entirely from underneath. Owners report doing the M340i on ramps. Use good jack stands and get a helper for lining up the pipe.

Do I need a new turbo gasket for a B58 downpipe?

We recommend one. It's BMW part 18328612538 (Toyota 17279-WAA02). Some pipes, like Active Autowerke's, come with it pre-installed. AMS says the original can be reused if most of the sealing face is intact.

Is the downpipe install different on xDrive?

The steps are the same. The front driveshaft crowds the space next to the downpipe, so it takes longer to get the old pipe out and the new one in. Many downpipes are one part for RWD and xDrive.

Will a B58 downpipe throw a check engine light?

It depends on the pipe and the tune. Race downpipes and many high-flow cats need a tune to keep the catalyst code away. Some catted pipes are sold as needing no tune. Check your pipe's listing and talk to your tuner.

What is the torque spec for the B58 downpipe V-band?

We couldn't find a published BMW value we trust. Torque it to the value in the instructions supplied with your downpipe or clamp, and recheck after a few heat cycles.

For the full build order, see the best B58 mods, in order. M340i owners should also read our M340i and M440i mods guide, and Supra owners our A90 Supra mods guide. Doing the charge pipe too? See the B58 charge pipe install guide.

Sources