The Akrapovic Slip-On exhaust system for the Porsche 911 is a superb system with a dual nature. By using the optional Wireless Kit, the driver can fully control the exhaust valves, which are controlled bu the car's electronics if no optional part is used. When the valves are closed, the 911 sounds deeper than stock, but not louder. When the valves are open, expect a completely oppositem pure racing sound, with adrenaline-pimping bangs while keeping away the droning sound.