2012-2015 KAWASAKI ZX14 M4 Retro Drag Slip-On Exhaust - Black This system utilizes the stock header assembly. Bolt on and slip-ons replace the stock restricted muffler resulting in better sound and an increase in power. Retro Drag Slip-On(s) in Black. M4 Performance Exhaust engineered the Retro Drag dual slip on exhaust system to offer an original exhaust that provides performance increase along with the obvious sick looks with the black ceramic coating. The look of the M4 Retro Drag dual exhaust is not the only thing separating it from the others, the sound produced from this exhaust announces pure power.