What is it?

‘Performance derivative’ is a much-abused automotive term. Which is probably why BMW’s M division, Audi’s Quattro and Mercedes’s AMG arm are all listed as independent companies, underling their collective seriousness of purpose.

The new CLS 63 AMG is a case in point. It receives a bespoke engine and transmission, a new front axle, substantially modified suspension and steering systems as well a unique damping system. The extensive styling changes inside and out are literally the icing on a seriously re-engineered cake. And AMG engineers have put over one million test kilometres into both the engine and the finished car.

It gets the company’s new M157 5.5-litre bi-turbo V8 engine which replaces AMG’s old 6.3-litre naturally-aspirated V8. The M157 (like all AMG motors, assembled by a single engineer) is more powerful, torquier and an amazing 32 per cent more economical than the outgoing engine. AMG has also developed its own ‘Speedshift MCT’ 7-speed transmission, which ditches a conventional - and laggy - torque convertor for a much more direct-feeling ‘wet start-up clutch’ which runs in a oil bath.

One of the most important aspects of the CLS’s development lies in the huge efforts that the company has put into the new electromechanical steering system. The 14:1 ratio is 22 percent quicker than the standard CLS, its is said to be extremely rigidly mounted and its control unit takes information from a wide range of sensors (including lateral acceleration and under and oversteer characteristics) to calculate the forces it feeds back to the wheel rim.

What’s it like?

And it’s the CLS 63’s steering response that strikes the driver as the car creeps away from standstill. At low speeds there’s a sense of uncanny, sharp-edged, precision humming through the wheel’s rim. It’s most unexpected, but a sensation that I’ve only associated with mid-engined supercars. (I’ve not gone mad, by the way. AMG boss Olla Källenius told me that Mercedes engineers who tried the 63 AMG, said the same thing.)

That extraordinary sensation continues as you drive along. While not uncomfortable, the AMG’s chassis telegraphs an amazing amount of information about the road surface to the seat and wheel. There’s a strong feeling of an almost unbushed connection with the road, but this mix doesn’t seem to be especially nervous or wearing over distances.

But it was on the winding mountain roads on the US/Mexican border that the CLS 63 really revealed its talents as a scalpel-sharp tool. Firstly, it is quite ridiculously easy place the front inside wheel on the very ragged edge of the road, allowing more confidence in swift progress. The driver gets a super-accurate sense of the position of the front wheels and the amazingly rigid front end means the AMG is exceptionally keen on turn-in. It pulls itself into and around corners with a surprising degree of aggression, creating very high lateral forces very quickly, which can be hard on your passenger.

The wide open spaces also allowed a little exploration of the 63’s huge, bombastic, performance, with its matching bombastic exhaust note. The engine’s delivery still has some of the flavour of natural aspiration, with the wallop building up across the rev range.

On the Mexican border one section of the road opened out into a huge, double width, racetrack-like downhill curve. As it bit into the bend, it was clear the CLS 63 AMG is the real deal.

Should I buy one?

This is a remarkable hybrid machine. At first glance it looks like it would be most at home outside the Beverley Wiltshire Hotel. In fact, it’s more than capable of enthusiastic track use. Even if you’re not a hot lap enthusiast, any skilled driver will deeply appreciate the car’s sheer engineering integrity and million-kilometer honed performance.