Which B58 Downpipe Fits My M340i, M440i or M240i? GEN1 vs GEN2 vs GEN3 LCI

Quick answer

If you are shopping for an AZ Motorsport B58 downpipe, do not choose by engine code alone. Choose by chassis, model year and AZM product generation.

For most older F-chassis B58 cars, use the AZM GEN1 B58 downpipe. For the first G-chassis M340i/M440i/M240i applications, use the AZM GEN2 B58 downpipe. For 2025+ LCI M340i and M440i applications listed by AZM, use the AZM GEN3 LCI B58 downpipe.

The common mistake is assuming that “B58” means every downpipe is interchangeable. It does not. Real buyers are asking exactly this on G20/G22 forums, especially when moving from a 2022 car into a 2025 LCI car.

Fitment table: AZM B58 downpipe lineup

Use this as a starting point, then confirm against the live product page before ordering because fitment pages and prices can change.

GEN1: F-chassis B58 cars

Choose the AZM GEN1 B58 downpipe if your car matches the older F-chassis fitment listed by AZ Motorsport: F22/F23 M240i, F30/F31 340i, F32/F33/F36 440i, plus the listed G30/G32/G11/G12 40i applications.

AZM lists the GEN1 product in Race (Catless) and High Flow (Catted) variants. The product page also lists 304 stainless steel construction, CNC-machined flanges or cast inlets, TIG welding, OEM mounting points and no cutting or welding required.

GEN2: early G-chassis M340i, M440i and M240i

Choose the AZM GEN2 B58 downpipe if your car is in the first G-chassis fitment group listed by AZM: 2019+ G20 M340i, 2021+ G22/G26 M440i or 2022+ G42 M240i. AZM also lists G05 X5 40i, G29 Z4 M40i and G30 540i under the GEN2 product.

This is the product many G20/G22/G42 buyers should check first. It is also where buyer confusion starts, because later LCI cars can share familiar model names while using different downpipe fitment.

GEN3 LCI: 2025+ M340i and M440i confusion

If your search is “b58 gen3 2025 downpipe m340i,” you are looking at the exact confusion this guide is meant to solve.

AZ Motorsport lists a separate GEN3 LCI downpipe for 2025+ G20/G21 M340i LCI and 2025+ G22/G26 M440i LCI. The same AZM GEN3 LCI product page also lists 2024+ G60 540i LCI, 2023+ G70 740i LCI, 2025+ G45 X3 50i LCI, 2024+ G05 X5 40i LCI, 2024+ G06 X6 40i LCI and 2023+ G07 X7 40i LCI.

Do not assume a GEN2 downpipe from a 2022 M340i will transfer directly to a 2025 M340i LCI. Forum buyers are asking about exactly that swap, and at least one thread discusses the 2025 B58TU2 / LCI design as different. Treat that forum discussion as a warning sign, not as the final authority: the final authority is the live AZM fitment list for the exact product.

What about a 2025+ G42 M240i?

AZM’s GEN2 product page lists 2022+ G42 M240i. The AZM GEN3 LCI product page, as checked for this brief, lists 2025+ G20/G21 M340i LCI and 2025+ G22/G26 M440i LCI, but it does not list G42 M240i on that GEN3 LCI page.

That means the safe buyer answer is: if you have a G42 M240i, start from the GEN2 listing, then verify your exact model year/VIN details with AZ Motorsport before ordering, especially for later model-year cars where forum buyers are reporting confusion.

Catless vs high-flow catted

AZM lists both Race (Catless) and High Flow (Catted) choices across the B58 downpipe lineup. The right choice depends on your build, tuning plan and where the car will be used.

Important: AZM’s B58 downpipe product pages state these parts are for closed-course competition / off-road race use only and are not legal for public-road or emissions-regulated vehicles in Canada or the United States. Do not treat “catted” as a legal guarantee. If the car is registered for road use, check the rules that apply where you live before buying or installing.

What a downpipe changes

AZM describes the B58 downpipes as direct bolt-on replacements designed to reduce backpressure, improve exhaust flow and support faster turbo spool, especially when paired with proper tuning. The product pages list 304 stainless steel construction, TIG welding, CNC-machined flanges or cast inlets, and compatibility with factory and most aftermarket exhaust systems where applicable.

This guide does not claim a specific horsepower gain because the brief did not find an AZM-sourced, model-specific dyno number for these exact variants. If a build needs a guaranteed power target, treat that as a tuning conversation, not a generic fitment claim.

Québec / Canada buyer notes

For Canadian buyers, AZ Motorsport’s advantage is not only the part itself. AZM ships from Québec and positions its downpipes as manufacturer-direct products with no customs fees in Canada. That matters when you are comparing a landed price against a US listing that may add exchange, brokerage, duties and delays.

For Québec winter use, the relevant sourced construction claim is 304 stainless steel. That is useful for corrosion resistance, but this brief did not find a salt-spray or winter durability test, so the guide should not overpromise winter performance.

Before you order: three checks

1. Match your chassis and model year to the AZM product generation.
2. Confirm whether your car is pre-LCI, LCI or later B58TU2 / GEN3 LCI.
3. Confirm variant choice, emissions/race-use restrictions and tuning plan before installing.

If you are unsure, contact AZ Motorsport with your VIN, model year, chassis code and whether your car is xDrive. That is faster than guessing from “B58” alone.