Exhaust› Exhaust Pipes, Systems and Components

MAD

S58 3.5-Inch Catless Downpipe

$299.00

SKU: MAD-047

In Stock
In Stock
Ships by Sep 12
Free Shipping over $200
$100 Minimum Order
30 Days Return
INSTALL DIFFICULTY
DIY PRO SHOP

Moderate — 2–4 hours

Overview

The MAD Fat Boy is a 3.5-inch catless downpipe designed for the BMW S58 engine. These downpipes replace restrictive stock catalytic converters to promote faster turbo spooling, increased airflow, and enhanced engine exhaust sound.

Constructed with smooth bends and an integrated flex pipe section, this system minimizes unwanted vibration and engine stress. It is compatible with both left-hand and right-hand drive configurations and carries a lifetime warranty.
Show original supplier description
The MAD Fat Boy is a 3.5-inch catless downpipe set engineered to maximize performance for the BMW S58 engine, specifically fitting 2021+ BMW M3 (G80), 2021+ BMW M4 (G82/G83), and 2023+ BMW M2 (G87) models. By eliminating the backpressure of stock catalytic converters, these downpipes allow for significantly improved turbo response and higher peak power potential. Featuring a 3.5-inch diameter that exceeds standard 3-inch alternatives, the system uses smooth, precision-formed bends to optimize exhaust flow. An integrated flex section is built into the construction to dampen engine vibrations and reduce stress on the exhaust system, ensuring long-term durability. This kit is fully compatible with both right-hand and left-hand drive vehicles. Designed as a direct performance upgrade, these downpipes support increased power output on both stock and upgraded turbo setups. The manufacturer includes a lifetime warranty covering defects and fitment to ensure consistent quality.

Product descriptions are provided by our supplier partners and may not always be perfectly accurate. Not sure this fits? or call (760) 282-4645 and we’ll verify before you order.

Fitment

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Specifications

BrandMAD
Part NumberMAD-047
CategoryExhaust

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Returns & Fitment

Built for enthusiasts. Every order is backed by our 30 day return window on eligible items. Unused and uninstalled products may be returned with approved RMA and no restocking fees when received in new condition. Orders placed through the MOTORMIA app with a complete build qualify for our Fitment Guarantee — free return shipping if the part doesn’t fit your exact setup. The guarantee covers fit only; installation must follow manufacturer instructions, and we recommend a qualified shop for parts marked Difficulty 4–5.

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Shipping

Orders are processed in 1–3 business days. In stock parts ship promptly from our partner network. Special-order items either aren’t currently stocked or are built to your spec — expect 4–6 weeks. If a part goes on backorder while your order is in the queue, we’ll reach out and work through discounted alternatives together.

Free shipping over $200 in the continental US. Alaska, Hawaii, U.S. territories (Puerto Rico, U.S. Virgin Islands, Guam, American Samoa, and the Northern Mariana Islands), and international orders carry surcharges — most appear at checkout. Some exceptions (LTL freight, or suppliers who quote freight only after we place the order) won’t. In those cases we’ll reach out with the exact charge before your order moves forward.

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