OneFastShop S55 Catless Downpipes | Power, Sound & Fitment for the F80 M3, F82 M4 & F87 M2

The BMW S55 is one of the best twin-turbo engines BMW has ever built, but from the factory it is held back by restrictive, heavily catted downpipes designed to meet emissions rather than make power. Swapping them is one of the most effective bolt-on upgrades you can make. The OneFastShop S55 3-inch catless downpipes strip out both factory catalytic converters to unlock the airflow, spool, and aggressive twin-turbo tone the S55 was built for. Here is what they do and who they fit.

What a Catless Downpipe Does on the S55

The downpipes are the section of exhaust that bolts directly to each turbo and routes spent gases into the rest of the system. On a stock S55, both downpipes carry catalytic converters that create backpressure and choke the twin-turbo setup. By replacing them with a full 3-inch catless design, exhaust gas exits the turbos far more freely. The result is quicker spool, sharper throttle response, and the headroom to support real power once the car is tuned.

Real-World Performance Gains

With proper tuning, these downpipes deliver a noticeable jump in output:

• +25 to +40 horsepower with a supporting tune
• Even larger gains on big-turbo and upgraded builds
• Dramatically faster turbo spool and sharper throttle response
• Stage 2+ tune ready, capable of supporting serious power builds

The full 3-inch diameter is maintained from each turbo outlet back, and a seamless cast v-band turbo transition keeps flow clean where it matters most. To realize these gains and keep the car running correctly, the downpipes should always be paired with a supporting tune.

The Sound

Removing the cats transforms the character of the S55. You get an aggressive twin-turbo tone from the turbo outlet back - deeper, louder, and far more purposeful than stock - along with more pronounced spool and blow-off character. Whether you run the factory exhaust or an aftermarket cat-back system, the downpipes are compatible with both, so you can build the exact sound you want.

Built to Last

These are not thin, mass-produced pipes. Each set is built from 304-grade stainless steel with CNC-machined flanges and hand TIG-welded joints, and integrated flex sections on both pipes absorb engine movement and reduce stress on the system. The seamless cast v-band turbo transition ensures a precise, leak-free fit, and the set is backed by a lifetime warranty on defects. They are compatible with both left-hand-drive and right-hand-drive cars. You can find these and our other downpipes in the OneFastShop catalog.

Fitment

This paired set is engineered for S55-equipped F-chassis M cars from 2015 to 2021:

• 2015-2018 BMW M3 (F80), including Competition
• 2015-2020 BMW M4 (F82), including Competition
• 2015-2020 BMW M4 Convertible (F83), including Competition
• 2019-2020 BMW M2 Competition (F87)
• 2020 BMW M2 CS (F87)

Important - S55 only: this kit fits S55-equipped vehicles only. The standard F87 M2 with the N55 engine uses a different downpipe and is not compatible. If you are unsure which engine your M2 has, confirm before ordering.

Installation

The downpipes are a direct bolt-on with no cutting required. Two turbo-to-downpipe gaskets are needed to seal the pipes to your factory turbos - our 3.5-inch turbo-to-downpipe gaskets for the S55 are sold separately in the exhaust gaskets collection, so add a pair to your order. As with any downpipe upgrade, plan to have the car tuned afterward to take full advantage of the added flow and to keep fueling and fault codes in check.

A Note on Legality

Catless downpipes are intended for off-road and track use only. Because they remove the catalytic converters, they are not legal for use on public roads and may not comply with emissions regulations in your area. Be sure to understand your local laws before installing.

Conclusion

If you want to wake up your S55-powered M3, M4, or M2, catless downpipes are one of the highest-impact bolt-ons available - more power, faster spool, and a genuinely aggressive twin-turbo soundtrack. Built from 304 stainless with a lifetime warranty and a true direct-fit design, the OneFastShop S55 catless downpipes are a straightforward way to get there. Pair them with a tune and the right gaskets, and your S55 will finally breathe the way BMW's engineers hinted at but never let it.

Frequently Asked Questions

How much power do S55 catless downpipes add?

With a supporting tune, expect roughly +25 to +40 horsepower, with larger gains on big-turbo and upgraded builds. Just as important, they noticeably improve turbo spool and throttle response.

Do these fit my M2?

They fit the S55-powered M2 Competition (2019-2020) and M2 CS (2020) only. The standard F87 M2 with the N55 engine requires a different downpipe and is not compatible. Confirm your engine before ordering.

Do I need a tune with catless downpipes?

Yes. A supporting tune is strongly recommended to realize the power gains and to keep fueling correct and fault codes away. The downpipes are Stage 2+ tune ready.

Will these work with my factory or aftermarket exhaust?

Yes. The downpipes are compatible with both OEM and aftermarket cat-back exhaust systems, so you can run them with your existing setup or pair them with a full aftermarket exhaust.

What do I need for installation?

The downpipes bolt on directly with no cutting required. You will need two turbo-to-downpipe gaskets to seal them to your factory turbos, which are sold separately. Plan for a tune afterward.

Are catless downpipes street legal?

No. Because they remove the catalytic converters, they are intended for off-road and track use only and are not legal for public road use or compliant with emissions regulations in many areas. Check your local laws first.