The G8x M3/M4 excels in nearly every aspect compared to its precursor, but the prevailing concern among enthusiasts lies in its sound quality. Similar to its predecessor, the S55 in the F8x, the S58 in the current generation still leaves room for improvement. While the stock sounds are a step up from the previous generation, they still have an excess of raspiness that fails to convey the refined aggression inherent to the brand's signature performance models. MAD remedies this shortcoming with a valved axle back exhaust system that delivers a deeper, more impactful note, and adds a level of amplification beyond the stock version. When paired with the optional single midpipe, it yields an even louder, smoother, and fuller sound.

To achieve the desired sound volume and tone befitting the G8x M3/M4, we increased the tubing size to 76mm (from the stock's 70mm), which reduces backpressure and allows a freer flow throughout the system. The larger piping diverges into multiple paths as it approaches the vehicle's rear, the choice of which is determined by the factory exhaust valves that are retained.

When the valves are closed, flow is directed into the MAD muffler, and exits through the two inner tips. This restricts noise during low-speed driving and produces a more subdued yet deeper sound. When the valves are open during high-load conditions, most gases bypass the muffler entirely for a near-straight pipe design, achieving maximum aural enjoyment. This harmonious balance satisfies a range of tastes and offers civility or passionate aggression as the situation demands. MAD has determined this combination to be appropriate for the brand's signature performance models that cater to discerning enthusiasts who want the best in all scenarios.

Visually, MAD's G8x M3/M4 exhaust is meticulously constructed entirely from T304 stainless steel and TIG welded for superior visual appeal and color. The entire system is brush finished for a perfect look straight out of the box. The attention to detail isn't limited to the unseen parts once the exhaust is installed; it extends to the exhaust tips as well. MAD's exhaust includes substantial quad 4.5-inch (114mm) clamp-on exhaust tips. Despite their large size on paper, the tips seamlessly integrate and fill the factory cut-outs, achieving the OEM+ look with an added touch of audible attitude.

Features:

• Connects to Factory Midpipe (Cutting required) or MAD Single Midpipe (No Cutting required)
• Maximum gains of +5 HP and +5 lb-ft of torque
• Pleasingly louder, sportier sound
• Drone abatement technologies reduce cabin resonance
• 4.5-inch (114mm) tips
• Larger diameter piping for increased flow (76mm vs. 70mm)
• 7-pounds lighter than the stock axle back (Stock: 44-pounds vs. MAD: 37-pounds)
• Reuses stock exhaust valve actuators, and the operation of exhaust valve is unchanged so the exhaust tone can be adjusted via the M-drive settings
• Includes extended valve harness 
• Computer-controlled exhaust valves are retained and limit noise during low-speed driving, and open fully during high-load conditions
• 100% 304 Stainless Steel construction
• Factory-like fitment with included mounting hardware