BMW B58 Catless Downpipe — Gen 1 vs Gen 2, Fitment & Power Gains
The B58 catless downpipe is the first hard-part most B58 owners buy, and for good reason: it removes the single biggest restriction in the factory exhaust and unlocks what a tune can actually do. This guide covers what a catless downpipe does, how to tell a Gen 1 from a Gen 2 B58 so you order the right part, the power you can realistically expect, and where an Australian owner stands on legality.
What a catless downpipe actually does
The downpipe is the section of exhaust that bolts straight to the turbo. On a factory B58 it houses a catalytic converter and a restrictive cast housing that chokes flow the moment you add boost.
A catless downpipe deletes the cat and replaces the cast section with a mandrel-bent stainless pipe. Three things change:
- Less backpressure — the turbo breathes out more freely, so it spools sooner and holds boost more consistently up top.
- Headroom for a tune — a Stage 1 (tune-only) B58 is limited by the stock exhaust. The downpipe is what makes Stage 2 possible.
- More sound — a deeper note and more turbo character, without going full straight-pipe.
Gen 1 vs Gen 2 B58 — which downpipe fits your car
This is the part people get wrong. BMW split the B58 into two generations, and they use different downpipe fitments. Check your build date and chassis before you order.
| B58 Gen 1 | B58 Gen 2 (B58TU) | |
|---|---|---|
| Years | 2016–2019 | 2019+ |
| Typical chassis | F20, F22, F30, F32, and early G-chassis (G11, G30, G32) | G20 M340i, G22 M440i, G42 M240i, G29 Z4, A90/A91 Supra |
| Common models | 340i, 440i, 540i (F-series) | M340i, M440i, M240i |
If you’re not sure which you’ve got, the quickest tell is the platform: F-chassis cars are Gen 1, the G-chassis M340i/M440i/M240i and the A90 Supra are Gen 2. When in doubt, send us your VIN or build date and we’ll confirm the right fitment before you buy.
How much power does a B58 downpipe add?
On its own, a catless downpipe is worth a modest gain and a noticeably better spool — the real numbers come when it’s paired with a tune. The downpipe’s job is to remove the ceiling so the tune can do its work.
- Stage 1 (tune only): strong gains on the stock exhaust, but the downpipe is still the limiter.
- Stage 2 (downpipe + tune): B58 owners typically see around +25–35 hp over Stage 1, plus better throttle response and more consistent power up top.
Exact figures depend on your fuel, boost target and supporting mods. Treat any single dyno number online with caution — gains vary between the lower-output and higher-output B58 variants.
Is a catless downpipe legal in Australia?
Straight answer: a catless downpipe is an emissions component delete, so it is for off-road and track use only and is not ADR-compliant for a registered road car. Removing the catalytic converter will fail an emissions or roadworthy inspection.
Plenty of owners run catless setups on dedicated track and competition cars, or hold a catted option for street use. We’d rather tell you that up front than have you find out at inspection time. If you need a street-friendly path, ask us before you order.
Fitting it
A B58 downpipe is a bolt-on job — no cutting or welding on a direct-fit part. It’s accessible from underneath, and most workshops knock it over in a couple of hours. Budget for new turbo-outlet hardware and expect a few heat cycles before the stainless settles in.
Unless you’re comfortable working under a hot exhaust and torquing to spec, it’s worth having a workshop fit it and clear any codes with your tune.
The EuroSpec B58 downpipe
Our BMW B58 catless downpipe is a direct OEM-fit part covering both Gen 1 and Gen 2 B58, built from 304 stainless and TIG-welded. It’s $550 AUD, held in Australian stock and dispatched fast — not drop-shipped from overseas with a month-long wait.
- 304 stainless, TIG-welded, mandrel-bent
- Direct OEM fitment — Gen 1 and Gen 2 B58
- Australian stock, fast dispatch, fitment backed by us
FAQ
Will a B58 downpipe fit my M340i?
Yes — the G20 M340i is a Gen 2 B58. Our downpipe is a direct fit for both Gen 1 and Gen 2, so it suits the M340i, M440i and M240i as well as the F-chassis 340i/440i.
Do I need a tune with a downpipe?
You should. A downpipe without a tune leaves most of the gain on the table and can throw a cat-efficiency code. The downpipe and tune are a package — that’s Stage 2.
Is a catless downpipe loud?
It’s louder and deeper than stock, with more turbo character, but it’s not a straight-pipe. Most owners find it a good balance of note and drone on the B58.
Gen 1 or Gen 2 — how do I know which I have?
Go by chassis: F-series (F30/F32 etc.) is Gen 1; the G-series M340i/M440i/M240i, G29 Z4 and A90 Supra are Gen 2. Still unsure? Send us your build date or VIN.
Does a downpipe void my warranty?
Fitting a catless downpipe and tune is a modification and can affect powertrain warranty claims. That’s a call each owner makes — we’re happy to talk through it.
The takeaway
A B58 catless downpipe is the part that turns a tune from “nice” into a genuine Stage 2 car — as long as you order the right generation and go in knowing it’s a track/off-road part. Get the fitment right and it’s the best-value hard part you’ll buy for the platform. Browse the EuroSpec B58 downpipe, or message us your chassis and we’ll confirm the fit.
