Taking the roof off of a car removes structural rigidity, which is why most of the world’s fastest cars have metal tops on them. Not that you can’t go fast in a ragtop—I mean, look at the new Brabus Rocket 900 Cabrio, for example, capable of speeds of better than 350 km/h (217 mph).

Yes, the new Mercedes-Benz S 65-based Rocket – good name – can rocket up to some incredible velocities, lack of a roof be darned. It takes the 6.3-litre V-12 just 3.9 seconds to get the car from a standing start to 100 km/h (62 mph), thanks in no small part to its 900 horsepower and 1,106 lb-ft of torque outputs. (Full disclosure: the max torque is electronically limited to 885 lb-ft.)

Those numbers make the Rocket 900 Cabrio the world’s fastest and most powerful street-legal four-seater convertible, a title it swiped from its older brother, the 850 Biturbo Cabrio.

Though the “Biturbo” was dropped from the name, the V-12 does still boast two induction-chargers hanging off of its exhausts, special units not found on the stock Benz. The factory 6.0-litre gets bored and stroked to its 6.3 litres of displacement as well, and a new custom intake is added in order to get that outstanding 900-horses figure.

It routes all that through a seven-speed automatic – paddle shifters let you switch gears manually, if you want – and 21-inch custom Monoblock wheels. (“King-sized” 22s are an option; the 0.6-inch lowering job is included, though.)

Also on the upgrade list are carbon-fibre aerodynamic lower body additions, which you can order fitted to your stock S 65. The interior comes modified to your taste, though “tailor-made noble wood components” cut from black ash are a standard trim upgrade.

The Brabus Rocket 900 Cabrio makes its world debut at the Frankfurt motor show this month.