MAD B58 Gen 3 Fat Boy 5" Catless Downpipe (2025+)
Pipe size 5 inch
Catalyst Catless
Application 2025+ B58 Gen 3
Build data

Specs that matter for this part

Hardware

Flow-focused exhaust path

Large-diameter tubing, smooth bends, and a flex section reduce restriction versus the factory exhaust path.

Validation

Catalyst configuration

Catless setup. Review local emissions requirements and product notes before street use.

Requirement

Direct bolt-on hardware

Designed to retain OEM-style fitment without cutting or welding on supported applications.

Downpipes can affect emissions readiness, sound level, and calibration needs. Review the product description before ordering.

This Gen‑3 Fat Boy downpipe features a massive 5‑inch diameter for improved exhaust gas velocity and a deeper, more aggressive exhaust tone. Made from premium 304 stainless steel, it is a direct bolt-on upgrade that delivers increased horsepower and torque and fits 2025+ BMW M340/M440 and the forthcoming X3 G45 and X4 G46 models

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