BMW F8X M3/M4 Valved Cat-Back Exhaust System

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

(T304 Stainless Steel or Grade 5 Titanium)

Overview

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.

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.

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

Why It Works

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

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

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

Sound & Control

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

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

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

Construction & Options

• Materials: T304 stainless steel or Grade 5 titanium.

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

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

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

Fitment

• 2015–2018 BMW M3 (F80)

• 2015–2020 BMW M4 Coupe (F82)

• 2015–2020 BMW M4 Convertible (F83)

Installation Notes

• Direct bolt-on; no cutting or welding required.

• 100% reversible—return to stock at any time.

• 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.

What’s Included

• 2.75" equal-length H-pipe mid-section

• 3.5" axle-back with quad-chamber muffler

• Electronic valve system with controller (OEM integration optional)

• All necessary clamps and hardware

Specifications

• Mid-Section Diameter: 2.75" equal-length with H-pipe

• Axle-Back Diameter: 3.5"

• Material: T304 stainless steel or Grade 5 titanium

• Valves: Electronic, rapid open/close

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

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

Important Information:

This product is intended for performance use and should be installed by a qualified professional.

It is the customer’s responsibility to ensure compatibility with their specific vehicle prior to purchase. If you are unsure, please contact us before ordering.

Gridline Custom Motorsports is not responsible for issues arising from incorrect installation, misuse, or improper product selection.

Due to the nature of performance parts, some items may be special order and subject to supplier availability and lead times.