| First Drive | Stuttgart, Germany | Mercedes-Benz S 63 AMG |

Great as AMG's high-revving 6.2-litre V8 is it never felt right in the S-Class. With the new S 63 AMG the badge remains the same, but the engine has changed, AMG swapping the naturally aspirated 6.2-litre V8 for a bi-turbo 5.5-litre of the same configuration. It's all been done in the name of economy - with a fuel consumption reduction of more than 25 percent - but power's up too.

In the Metal

The S 63 is a relatively subtle looker, with AMG revisions restricted to below the bumper. There are deeper front air intakes, while side skirts and a deeper rear bumper visually lower the big saloon on the road. Large split-rim five-spoke AMG alloy wheels and V8 bi-turbo badging on the front wings denote this performance model, with the most obvious change over its more sedate relatives being the rather extrovert chrome-finished quad tailpipes under the rear bumper.

Inside it's all familiar S-Class, though the seats hold you a bit more tightly and the screens flash up the AMG logo on start up before displaying the infotainment and instrumentation.

What you get for your Money

Sitting at the top of the S-Class range the S 63 AMG comes with almost everything imaginable as standard. The new car debuts some innovative new safety equipment, including Lane Keeping Assist and Blindspot Assist - both of which actively brake wheels to steer the S-Class away from danger. Clever stuff. Key here though is the 5.5-litre bi-turbo engine mated to an AMG Speedshift seven-speed automatic transmission, AMG Sports suspension and the optional (£7,890) Performance Package, which boosts output from an already heady 536- to 563bhp and increases peak torque from 590- to 664lb.ft. With the Performance Pack you also get carbon fibre trim, an AMG steering wheel, a raised 186mph top speed and a day of training at an AMG 'Power and Passion' course.

Driving it

The bi-turbo 5.5-litre V8 rouses without quite the histrionics that defines its 6.2-litre V8 predecessor. It immediately feels more suited to the S's demeanour as a result, the high-revving racecar-like 6.2 always ill-suited to the luxury car surroundings of the S-Class. The 5.5-litre bi-turbo - which confusingly retains the S 63 badge regardless of the engine's actual capacity - is more muted on start up, and pulls away without the need for as many revs.

It's that low down torque that defines the new 5.5-litre bi-turbo engine; there are absolutely masses of it. Peak torque in the Performance Pack car is available from 2,250- to 3,750rpm, the enormous twisting force allowing the S-Class to effortlessly waft along on low revs. It's quite at odds to the experience of the old S 63, which needed its engine wringing out for it to deliver the expected performance.

Push the accelerator into the plush carpet and the Performance Pack equipped S 63 shaves 0.1 of a second off the standard S 63's 4.5-second 0-62mph time. It delivers this with supreme ease, the S 63's new unit delivering massive punch and enormous flexibility. It makes the performance on offer so much more accessible, making the paddles for the AMG Speedshift seven-speed sports automatic gearbox largely redundant. Leave it in Drive and it's wickedly fast, it not needing you to intervene as you had to in the old car to maintain revs for the engine to produce its best.

AMG's tweaked Active Body Control suspension provides great control mixed with a ride that manages to cosset as an S-Class should. There's very little roll in corners and the steering is light and accurate, though not exactly loaded with feel. It's the engine though that defines the experience. The bi-turbo V8's huge torque allows it to pull off the trick of low-rev ease to imbue the S 63 with its necessarily effortless luxury, yet provides big punch and redline-seeking eagerness - all overlaid with a fruity sounding exhaust note - justifying its AMG status.

Worth Noting

Unlike its 6.2-litre predecessor the 5.5-litre bi-turbo isn't an entirely AMG design - it shares some parts with Mercedes' engine line-up. Featuring start-stop along with a number of other economy enhancing technology, the S 63 returns 26.9mpg on the official combined cycle and just 244g/km of CO₂ - hugely impressive for such a large, high-performance saloon.

Summary

AMG's 6.2-litre V8 always felt a bit incongruous in the S 63 and this new 5.5-litre bi-turbo engine only underlines that. Powered by it the S 63 feels like an entirely different car, one that still boasts AMG's usual loony performance, but mixes it with luxury car civility. It's so different in character is should perhaps wear a new name - surely AMG has some old '55' badges lying about in a box somewhere?