BMW built one of the greatest engines on the planet with the S58. 500 horsepower, twin turbos, and a sound that makes grown men emotional. Then they shipped it with restrictive factory downpipes that choke the whole thing out.
That changes today.
We just installed a set of MAD Catless Downpipes on a G80 M3 and the difference is night and day. If you own an M3 or M4 and you've been on the fence about this upgrade — keep reading.
Why the Factory Downpipes Are Holding Your S58 Back
From the factory, BMW equips the G80 M3 with downpipes that prioritize emissions compliance over performance. The catalytic converters inside create a significant restriction in exhaust flow — and when you're pushing air through a 500hp twin-turbo engine, restriction is the enemy.
The MAD Catless Downpipes eliminate that restriction completely. No cats. Zero choke points. Just a straight, free-flowing path for your exhaust gases. The difference in the opening size between stock and MAD is something you have to see to believe — and once you hear the car after the swap, there's no going back.
What You'll Need Before You Start
This isn't a beginner job, but it's very doable in a home garage with the right tools. Before you get under the car, have these ready:
- MAD Catless Downpipes (G80/G82 specific fitment)
- 10mm, 13mm, 16mm, and 21mm sockets
- Ratchet wrench (13mm — essential for the Vband clamps)
- Pry bar (for splitting the Vband clamps)
- O2 sensor socket
- Plenty of patience — there are more hidden bolts on this job than you'd expect
The Install Breakdown
Step 1 — Clear the Engine Bay
Start by pulling the strut brace. It's a straightforward removal but necessary to give yourself the clearance to work properly. The engine cover comes off next so you can actually see what you're dealing with.
Step 2 — Locate All Your O2 Sensors First
This is where a lot of people get caught out. There are two O2 sensors per side plus an additional one for the front cat — and that last one is tucked right under the front turbo and easy to miss. Find and disconnect all of them before you start pulling anything else. These wires are also clipped to the head, so free them up now or they'll fight you during removal.
Pro tip: don't force any connectors. These are expensive sensors and they're finicky.
Step 3 — Drop the Undercarriage Shields
There's a lot of hardware underneath this car. Expect a mix of 16mm and 10mm bolts — and heads up, there are additional 21mm bolts hiding under the shields that are easy to miss if you're not looking for them.
The bulk of this job is on the passenger side, which gives you better access to everything you need.
Step 4 — Tackle the Vband Clamps
The front and rear Vband clamps are what hold the downpipes in place. Use a 13mm ratchet wrench to remove the bolt, then use a pry bar to split the clamp for clean removal. It's also worth pulling the intermediate pipe section to create more room — the extra space makes the swap significantly easier.
Step 5 — Pull the Stock Downpipes
With everything disconnected and the clamps loose, the stock downpipes come out. Take a second here to hold them up against the MAD units side by side. The difference in the opening size is immediately obvious — this is exactly what's been restricting your engine.
Step 6 — Install the MAD Downpipes
Swap your O2 sensors over to the new downpipes — both sides — and don't skip that third sensor that's easy to forget. Drop the MADs in, get both Vband clamps snugged up tight, and work your way back up reconnecting everything you touched.
One thing to double check: make sure every wire that was clipped to a bracket gets re-clipped. A loose wire near a hot exhaust is a problem you don't want.
Step 7 — Button It Up and Fire It Up
Shields back on, engine bay back together, start it up. The S58 sounds absolutely insane with these downpipes on. It's not subtle. Your neighbors will know.
Is It Worth It?
If you own a G80 M3 or G82 M4 and you care about getting the most out of the S58, yes — without question. The MAD Catless Downpipes are one of the highest-impact bolt-on modifications you can do. You're freeing up an engine that BMW deliberately restricted, and the sound alone justifies the install.
Just be aware — catless downpipes aren't street legal in all states and will trigger a check engine light without a tune. Make sure you're running this on a track-focused build or pair it with an appropriate tune for your setup.
Watch the Full Install
Want to see the whole process from start to finish — including that first startup? Watch the full video below and hear exactly what the S58 sounds like when it's finally unleashed!