When the Brabus Rocket Cabrio makes its official debut at the Frankfurt Auto Show this month, it will do so as the world’s fastest and most powerful convertible.

The all-new Ferrari Portofino, which is getting ready to make its global debut in Frankfurt, can boast space for four, a retractable hard top, a twin turbocharged 600hp V8, a 0-100km/h time of 3.5 seconds and a 199mph top speed.

But those figures pale into insignificance alongside the latest creation from the world’s top Mercedes tuning company.

Taking the already impressive Mercedes S 65 S-Class cabriolet as its starting point, to create the Rocket, Brabus has had to increase the donor car’s engine displacement to 6.3 liters, add a new crankshaft, forge new pistons and develop new conrods, change how the engine breathes, add larger turbos and compressor unit and redesign the exhaust manifolds.

But in doing so they have built a genuine luxury convertible with ample room for four adult passengers that can also go from 0-100km/h in 3.9 seconds and on to a top speed well in excess of 217mph.

This is partly down to the fact that the rebuilt engine now sends 900hp to the rear wheels and offers the driver 1500Nm of torque to play with. But it’s also because Brabus has spent countless hours in the wind tunnel developing a unique aerodynamics package for the car.

And to ensure that the car can deliver on those figures on a regular, reliable basis, Brabus has rebuilt the 7-speed automatic transmission to handle the extra power, added a tougher limited slip differential, and to make certain that it doesn’t completely live up to its name, has changed the car’s aerodynamic profile at the front so that the front axle won’t lift under rapid acceleration or when nearing its top speed.

The company’s craftsmen have also been busy with the interior, replacing the stock wooden veneers with ones hand-shaped from black ash and giving the seats and door panels a unique two-color leather finish. And of course, because the car is now so much faster than the original, Brabus has had to upgrade the speedometer. It now goes up to 250mph.

The Rocket can be ordered as a complete car or as a list of individual upgrades to an existing S 65 and, because it’s a Brabus creation, it comes with a three-year warranty.