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BMW F8X M3/M4 Valved Cat-Back Exhaust System

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Equal-Length 2.75″ Mid-Section with H-Pipe and 3.5″ Axle-Back

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(T304 Stainless Steel or Grade 5 Titanium)

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Overview

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The S55 engine powering the BMW F8X M3 and M4 is a performance masterpiece, but its stock exhaust note has long been criticized for excessive rasp and a lack of tonal depth. The Valvetronic Designs Equal-Length Valved Cat-Back is the definitive solution—eliminating the factory harshness and unlocking the rich, balanced sound the S55 was always capable of producing.

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This system features a 2.75-inch equal-length mid-section with an H-pipe feeding into a 3.5-inch axle-back. The equal-length design smooths the exhaust tone across the rev range while preserving the aggressive character owners love. With valves open, gases exit freely from the passenger-side tips for maximum volume and performance. With valves closed, flow is routed through our quad-chamber muffler to the driver-side tips for a quieter, more refined note—ideal for daily driving.

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No cutting or welding is required—this is a true direct bolt-on system designed to mount to factory points.

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Why It Works

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  Equal-Length Mid-Section: Balances pulses for a cleaner, smoother tone without losing aggression.

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  H-Pipe Design: Improves scavenging for a fuller, more refined sound.

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  Dual-Mode Operation: Raw and loud (open) or subdued and civilized (closed).

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Sound & Control

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  Valves Open: Aggressive, free-breathing tone with reduced rasp and improved high-rpm clarity.

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  Valves Closed: Stock-like sound levels for stealthy driving.

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  Electronic Valve Control: Includes standalone controller; OEM integration available.

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Construction & Options

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  Materials: T304 stainless steel or Grade 5 titanium.

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  Weight Savings: –21.7 lb (Stainless) / –49.2 lb (Titanium) vs. OEM.

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  Craftsmanship: Precision TIG welds and fully mandrel-bent tubing for maximum flow.

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  Tips: Multiple premium finish options to complement your M3 or M4.

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Fitment

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  2015–2018 BMW M3 (F80)

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  2015–2020 BMW M4 Coupe (F82)

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  2015–2020 BMW M4 Convertible (F83)

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Installation Notes

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  Direct bolt-on; no cutting or welding required.

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  100% reversible—return to stock at any time.

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  Note for S55 Owners: On free-flow/race downpipes, “2k rpm rasp” may be present during low-rpm shifts. For the most refined tone, we recommend high-flow (200 cell) catalytic converters.

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What’s Included

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  2.75″ equal-length H-pipe mid-section

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  3.5″ axle-back with quad-chamber muffler

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  Electronic valve system with controller (OEM integration optional)

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  All necessary clamps and hardware

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Specifications

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  Mid-Section Diameter: 2.75″ equal-length with H-pipe

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  Axle-Back Diameter: 3.5″

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  Material: T304 stainless steel or Grade 5 titanium

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  Valves: Electronic, rapid open/close

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  Weight Savings: –21.7 lb (Stainless) / –49.2 lb (Titanium) vs. OEM

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  Design: Quad-chamber muffler for refined closed-valve tone

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