MAD BMW S58 4" Fat Boy Single Midpipe M3 M4 G80 G82

In Stock: Ships in 1-2 business days
Available to Order: Ships in 3-4 Weeks

Looking to unlock the full potential of your G8X exhaust setup?

The factory mid pipe is smaller and holds back the true character of the S58 — especially once you start adding power.

The MAD 4” FATBOY Midpipe eliminates that restriction with an oversized, free-flowing design built for maximum performance and sound.

This isn’t just an upgrade — it’s a complete transformation of how your car breathes and sounds.

Deep.
Aggressive.
Unfiltered.

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Why this Midpipe

The 4” FATBOY design is all about one thing — flow.

With a full-length 4” center section and a minimum 3” diameter throughout, this midpipe removes the bottlenecks found in the OEM system and even smaller aftermarket options.

The result:

• Noticeably deeper tone
• Increased volume without the “tinny” sound
• Reduced rasp compared to typical non-res setups
• A more raw, aggressive exhaust note that actually matches the car’s performance

Even when paired with catless downpipes, this setup holds its composure while still delivering that raw, unfiltered experience.

If you’re tired of muted or overly refined setups, this is the one that finally wakes the car up.

Maximum flow.
Maximum presence.
No compromise.

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Installation Overview

• Uses OEM cut location for straightforward installation
• Clamp-on design allows for reversibility
• Includes reducer couplers for multiple axle-back setups
• Professional installation recommended

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Fitment

BMW G8X Platform:

• G80 M3
• G81 M3 Touring
• G82 M4
• G83 M4 Convertible

Compatible with factory rear exhaust and most aftermarket axle-back systems.

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Construction

• Full-Length 4” Single Midpipe Design
• Minimum 3” Diameter Throughout
• 304 Stainless Steel Construction
• Mandrel Bent for Maximum Flow
• OEM-Style Clamp Design for Easy Install
• Includes 3” and 2.75” Reducer Couplers

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What's Included

• MAD 4” FATBOY Midpipe
• Brace
• Reducer Couplers (3” and 2.75”)
• Clamps and Required Hardware

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Warranty & Returns

• Eligible for a 90-day return window if unused, uninstalled, and in original condition
• Backed by a lifetime warranty on defects and fitment

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Automaz Approved

Not all “loud” setups sound good — and that’s where this one stands out.

The FATBOY Midpipe delivers the kind of deep, aggressive tone most setups fail to achieve, while maintaining a clean, controlled sound profile even at higher power levels.

If you want maximum flow and a raw, dominant exhaust note — this is it.