Kristiansund, Norway * Unlike the financial industry, even the most profligate of automakers are being socially responsible and minding their Ps and Qs these days.

Complain, if you must, that the always cynical auto industry is more concerned with the image of being green than actually changing its hue, or that their recent environmental interest is bit like Tiger Woods' mistress's concern about the welfare of the once-dominant golfer's family, but at least they're going through the motions, which is more than can be said for the folks over at Goldman Sachs.

Even the most ardent hedonists - and Mercedes' AMG tuning arm is among the most shameless of bon vivants - are looking to minimize their footprint.

That is, of course, as long as there's no sacrifice in performance or luxury. Caligula will always demand a smorgasbord; his public relations expert is just making sure the scraps are parcelled out to the unworthy.

This demand to marry (relative) frugality with its traditionally over-the- top performance is the motivation behind AMG phasing out the naturally aspirated, 525-horsepower 6.2-litre V8 that it only so recently developed. In its stead, it's come up with a 5.5L turbocharged powerhouse that pumps out even more power - 544 ponies (571 hp if you order the optional performance package).

``Now, wait a minute,'' I hear you saying. ``What a load of hooey. More horsepower doesn't sound very green. Mercedes is feeding you a line and now you're trying to feed it to me.''

Although it might not initially pass the smell test, Mercedes is not wallowing in dung. Yes, it's true that, all things being equal, any internal- combustion gasoline engine with more power will consume more fuel.

But, as anyone who ever tried to lob a jumper over Manute Bol or run an election campaign against a Kennedy can attest, things are never equal.

For one thing, engines are seldom called on to produce their peak power for any significant periods of time. So, while Mercedes' high-revving, naturally aspirated 6.2L and the 2011 S63's new 5.5L twin-turbocharged V8s probably have similar fuel consumption when they are producing their 500-plus peak horsepower, how they act when they're noodling around at 100 kilometres an hour is dramatically different.

You see, once those turbochargers stop force-feeding fuel and air, the S63's new V8 reverts to being a normal 5.5L V8 engine, which, displacing 747 fewer cubic centimetres, is significantly more frugal than the outgoing 6.2L.

Throw in other advancements such as direct injection and more efficient ancillaries - fuel pump, alternator, etc. - and the new S63 boasts 25% better fuel economy (10.5 litres per 100 kilometres versus 14.4 L/100 km in the European driving cycle) over the 6.2L version. Mercedes also notes that the turbocharged engine's increased torque (586 pound-feet for the regular version, 660 for the performance package) is available as low as 2,000 rpm, which means the engine can be shifted into a taller gear sooner, keeping engine revs and fuel consumption to a minimum.

But that sensation of overwhelming torque is also the reason the S63 feels like a sprinter in a lineman's body. Thanks to a bounty of pound-feet, the rather heavy S63 (Mercedes has released no official figure, but the full-sized sedan probably exceeds 2,200 kilograms) still scoots to 100 kilometres an hour in 4.5 seconds (4.4 if the aforementioned performance package has been ordered) compared with the outgoing model's 4.6 seconds.

Certainly, there's a whole bunch less drama involved. Where punching the old 6.2's throttle resulted in a flurry of revs as well as mind-boggling acceleration, the new S63 always seems to be loafing even when it's accelerating hard enough to pin you back in the seat. Mat the throttle and there's none of the traditional turbo lag while the engine gathers up its skirt for the impending sprint. Indeed, from inside the cabin, there's very little sensation of the engine working hard. (Passersby, however, could easily be forgiven for mistaking the S63's exhaust note for a McLaren SLR).

Yet, throttle response is so immediate that you'd swear the 5.5L's throttle plate is hard-wired to your cranium rather than through the gas pedal. Even at 1,500 rpm - barely above idle - the S63 is pumping out almost 500 pound-feet, more than the 6.2L has at its peak. Ditto the latest Porsche 911 Turbo.

Playing a huge part in the enhanced powertrain is a new seven-speed Multi- Clutch Transmission (MCT), which is making the rounds in Mercedes' sportier bolides. Based on the automatic with the same number of speeds, the MCT replaces the automatic's traditional torque converter with a wet multi-plate clutch (as used in most motorcycles). It shifts far more quickly than the automatic, yet is all but as smooth and, when in manual mode, fairly emulates the dual-clutch manuals popularized by Audi. It can blip the throttle for downshifts and, as a further concession toward economy and environmentalism, is equipped with a stop-start function that shuts down the engine at stoplights.

That's about it for changes to the new S63. Having improved performance slightly and fuel economy dramatically, AMG engineers can congratulate themselves on a job well done. That said, it's not a sure thing the new 5.5L twin-turbo will supplant the 6.2L in all of AMG's ``63'' offerings. The company claims the turbo engine is ideal for powering big, thundering sedans such as the S-Class, but the naturally aspirated 6.2L's more precise throttle response is still well suited to smaller, sportier models such as the C-Class. Perhaps, then, that's the new definition of automobile manufacturing hedonism - two engines with the same number of pistons, roughly the same power output and sporting exactly the same ``63'' model designation. The rest of the world tries to cut the number of engines it manufactures - AMG proliferates.

National Post

dbooth@nationalpost.com