N55 CATTED DOWNPIPE - F3X - 4" EWG

A downpipe is the single best hardware upgrade for getting real power out of an N55-powered F3X BMW, and the ARM N55 Catted Downpipe delivers the same gains as a catless pipe with far less exhaust odor. The factory downpipe ships with a restrictive catalyst that strangles flow; replacing it unlocks power, quickens spool, opens the door to Stage 2+ tuning, and adds volume — all at once. Expect up to 23whp and 29wtq.

Highlights

• Gain up to 23whp / 29wtq
• Faster turbo spool
• Improved exhaust sound
• Supports Stage 2+ tuning
• SS304 stainless steel

Construction

The downpipe is mandrel-bent from SS304 stainless and backed by the ARM Motorsports lifetime warranty. It starts at 4" at the precision CNC-machined turbo v-band, steps up to a 5" 200-cell sport catalyst, then tapers to a flared joint that matches the stock midpipe v-band exactly. Two O2 sensor bungs let you reinstall the factory oxygen sensors, and they sit higher on the pipe so you won't stretch the sensor wires during install. A tune or CEL delete is required to keep the check engine light off.

Flashing Stage 2+

By freeing up exhaust flow, this downpipe preps your F-Series for higher-boost tunes — if you already run software for your N55, those files are likely already loaded and waiting for you to flash after install. Most Stage 2 tunes also want a front-mount intercooler; if you don't have one yet, look at our F3X FMIC. Stage 2 N55s typically see around 400whp and 400wtq.

Improved exhaust sound

The downpipe accounts for roughly 20% of the exhaust system, so upgrading it produces a clear bump in volume — especially at full throttle and on cold starts. Want more? It pairs with any aftermarket exhaust that connects to the stock N55 downpipe.

In the box

• ARM N55 Catted Downpipe

Fitment

Fits the vehicles below equipped with the 4" EWG turbocharger only.

Backed by ARM Motorsports' lifetime warranty against defects in craftsmanship and fitment.

Emissions disclaimer: This product is not legal for sale or use on pollution-controlled vehicles operated on public roads and is intended for off-road, race, or closed-course competition use only. You are responsible for compliance with all applicable emissions laws; use on public roads may violate the Federal Clean Air Act (42 U.S.C. § 7522) and similar state laws. Please check your local laws before purchase and installation.

Ships from our Vancouver shop — KORE SPEED is proudly Canadian-owned, with no surprise cross-border duties for Canadian buyers. Questions on fitment? Email support@korespeed.com.