MERCEDES-BENZ has lifted the lid on its fire-breathing new SL 63 AMG roadster with the promise of more power, better dynamics and a whopping 30 per cent improvement in fuel efficiency.

The new model comes with a twin turbocharged V8 engine, an enhanced AMG sports suspension, new speed-sensitive sports steering, high-performance brakes and a speedshift 7-speed sports transmission.

And thanks to its aluminium bodyshell, similar to that of the SLS AMG super sports car, the SL's weight has been reduced by 125 kilograms.

For the first time, the SL 63 AMG is available with a choice of two power outputs, the AMG 5.5-litre V8 'biturbo' engine delivering 537bhp and 800 Nm of torque.

But if the AMG Performance package is specified, the figures rise to 564bhp and 900 Nm - more power than any other competitor in its segment.

The result is savage performance with acceleration from 0-62mph in 4.3 or 4.2 seconds, and to 125mph in 12.9 or 12.6 seconds respectively.

Top speed is an electronically limited 155mph, though this rises to 186mph, also governed, with the AMG Performance package on board.

Combined consumption comes in at 28.5mpg for both power outputs - a 30 per cent improvement over the outgoing model.

And Mercedes says that the car's crash-optimised structure, a standard-fit PRE-SAFE set-up plus assistance systems on a par with those of the S-Class make the SL the world's safest roadster.

Mercedes-AMG chief Ola Kallenius said: "The new SL 63 AMG is yet another masterpiece from Mercedes-AMG. Be it driving dynamics, lightweight construction or efficiency - the SL 63 AMG represents a giant leap forward.

"Following on from the SLS AMG Roadster and the SLK 55 AMG, it now makes our unrivalled roadster family practically complete."

Sales are due to start in late summer, though UK specification and prices have yet to be announced.