BMW F80 M3/F82 M4 - Resonated (Quieter) Secondary Catalyst Delete - For Fitment to MilltekMilltek Sport Large Bore Downpipes are perfect when looking to improve both performance and sound. These downpipes are fabricated with a larger diameter than standard OEM parts, meaning that there is significantly more space for more gas to exit the engine and pass through, increasing efficiency. Used with our Catalyst Bypass Pipe, you can expect significant power gain without any restriction on gas flow made by a catalyst. All our performance exhaust