Overall rating:

The engine swap might make the badge even more confusing - the E 63 AMG has gone from a 6.2- to a twin-turbo 5.5-litre V8 - but the move otherwise makes perfect sense: more kick using far less fuel. It's even more dichotomous than before, with a breathtaking turn of pace and sharpness, yet very good manners indeed.

Key Facts

Pricing: £74,000 (approx)
Engine: 5.5-litre twin-turbo V8 petrol
Transmission: seven-speed automatic, rear-wheel drive
Body style: four-door saloon
Rivals: BMW M5, Porsche Panamera S, Maserati Quattroporte
CO₂ emissions: 230g/km
Combined economy: 28.8mpg
Top speed: 155mph (limited)
0-62mph: 4.3 seconds
Power: 518bhp at 5,250rpm
Torque: 516lb.ft at 1,750rpm
Weight: 1,840kg
On sale: September 2011

In the Metal:

From a distance the AMG looks little different to any E-Class, but Beelzebub's in the detail. Anybody who knows anything or something about cars will spot the four flush tailpipes and know what this is. The Performance Pack adds mirror caps, a lip spoiler, splitter and rear valance all in yummy unpainted carbon fibre - and the car looks all the better for it.

Despite a complete lack of visual changes with this engine swap, the bores among you will spot the new 'V8 biturbo' engine designations on the flanks, and from the inside the new steering wheel and gear selector. We especially like the ornate embossing of the latter, and enjoy that the former's half Alcantara, half leather covering is a lovely poetic metaphor for the car's bi-polar nature.

Driving it:

When you read '5.5-litre twin-turbo V8' you don't naturally link that collection of words with lethargy. You probably link it with a sort of giddy trepidation. The giddiness because it will clearly be quicker than a Lord Sugar putdown, but the trepidation because it might be quite 'all-then-nothing' in the power delivery, and thus lacking character.

Not so. For a unit with so much torque (52lb.ft more than the current E 63, and power is the same), it doesn't half like to rev. It won't hit the 7,000rpm birdsong of the car it replaces, but it's got lungs, and it still does the good stuff like sounding maniacal at the top end, and coughing its guts through the tailpipes on downshifts.

It's a given that the overall ride compliancy will suffer somewhat in a super saloon with 525bhp and track aspirations, but Mercedes' adaptive damping setup works well. Each stage of the three-tiered damping - manually switchable and linked to the variable steering weight - differs noticeably, but all sit well in the middle of the two extremes of spongy limo and fossilised track car.

But on the road (as opposed to the track) it's the steering settings and throttle response (also variable) that most change to the way the 63 feels. Given the rack is electric, and that its weighting varies depending on both speed and damper settings, it's remarkably organic and intuitive. Kickback is progressive and natural, with no self-centring effect. The only real issue we have is with the speed of paddle-induced manual up-shifts, which are far too lazy and in contrast to an otherwise snappy seven-speed auto.

It's on the track that the 63's idiot-proof levels of grip, balance and all-round chassis communication really shine through. It takes significant speed to get it washing into understeer, and significant throttle abuse to coax steer of the opposite type. It has a lovely lightness of touch and agility coupled to a feeling that it's being pressed bloody hard into the ground. Good combo.

What you get for your Money:

Equipment levels in this end of the market are fairly academic - and Mercedes is currently finalising them anyway. The drop in CO₂ and consumption this engine offers is a gift horse: 6.4 more miles per gallon and 65g/km less CO₂.

Mercedes UK is currently figuring out the exact price, but it's a fair bet it'll be unchanged from the £74,000 estimate, because that's what's happened in Germany where the car goes on sale first. Given the development costs that will have gone into this 5.5-litre engine, hand built by a man with his own little cart in Affalterbach, that's a bonus too.

Worth Noting

Mercedes will offer a performance pack that adds, as well as the aforementioned carbon fibre bits, a Queen's stable worth of extra horses: 31, to be precise. The 549bhp car also gets 74lb.ft more torque, so it hits 62mph 0.1 seconds quicker. Order it, we say.

Summary

For all Mercedes says this engine swap is about hitting emissions targets, we all know that the company has one eye on the recently unveiled twin-turbo BMW M5, which is bound to be all kinds of awesome. But who cares the motivation, because the result is a faster, cleaner AMG whose quickness is more easily accessible, and whose chassis is wonderfully tractable. The M5 had better live up to the hype.