This video features a stunning Mercedes-Benz GT S GT4 equipped with PER4MANCE Industries exhaust system, upgraded turbochargers, downpipes and carbon bodykit. Result is a 728HP rocket machine! It got a custom build fully variable exhaust system, where you can open and close the valves! You can see and hear the GT-S start up its 4.0-litre twin turbo V8, revving multiple times and then accelerating on a 1/4 Mile drag race against an Audi R8! You clearly can hear the difference when the valves are open, so amazingly loud!