Ostensibly, the ongoing switch in the luxury segment from large, naturally aspirated engines to smaller turbocharged ones is all about increasing fuel economy. The concept is simple: reduce the displacement of the engine so that fuel consumption during everyday driving is minimised and then add a turbocharger so that, on demand, said smaller engine can produce more power. Any performance enhancement, if one listens to the corporate publicity wonks, is supposed to be secondary. In reality, the increase in performance is the most obvious difference. Take Mercedes\'s latest upgrade to the S550 as an example. Last year\'s version was powered by a 5.5L normally aspirated V8; the 2012 S550, meanwhile, sees a twice-turbocharged 4.6L V8 under the bonnet (Mercedes maintains the previous \"550\" designation because a] it prevents confusion and b] it sees the blown 4.6 as \"equivalent\" to 5.5L). One could, one supposes, try to pawn off the new car\'s 47 extra horsepower (429 in all) as a largely inconsequential advantage in a monster luxury saloon that weighs 2,075kg, but trying to relegate the new turbocharged engine\'s extra 169Nm of torque (700Nm in all), taking it to 100kph in less than five seconds as a mere by-product, stretches the credibility of even the most silver-tongued public relations hack. The real benefit to all this turbocharged muscle, however, is not in how quick the big Merc accelerates but how all that performance is dispensed. Again, the extra 47hp matters not; the big news is that extra 169Nm of torque and when and how it\'s produced. Being twice turbo\'ed - two small turbochargers are more efficient at low speeds than one large one - means there is simply bucket loads of torque at these same low speeds. In fact, low-rpm torque is so prodigious that the engine usually shifts around 2,000rpm. Three thousand rpm is seldom needed and, except for one quick burst (only for verification of performance, of course), I never took the car over 4,000rpm. By that time I was accelerating so hard that I was starting to scare Corvette drivers. And, even then, the powerful, low-revving engine seemed like it was loafing as if, despite the telephone poles blinding by, grandma was at the wheel driving to the shops for groceries. And so, despite those boasts of both five-second-flat acceleration times and frugal fuel consumption, it is this effortless ability to stay ahead of traffic that is the S550\'s most entreating character. Mercedes-Benz has always calibrated its automatic transmissions for reluctant downshifts, the theory being that kicking down a gear was an abrupt intrusion into what was supposed to be a seamlessly smooth ride. The problem was, for those of us with, er, tighter schedules, the lack of acceleration would encourage us to dig even deeper into the throttle until, when the trannie finally did downshift, the resultant flurry of revs and hard gear change really was abrupt. The new powertrain, however, is so tremendously powerful that it hardly ever needs to downshift. Indeed, I kept the engine in its \"economy\" mode (surely an oxymoron in a 429hp automobile), which deliberately restricts downshifts, and still the S550 powered relentlessly ahead like Kirstie Alley heading for the buffet table. Indeed, though the S550 gets the latest iteration of Mercedes\' seven-speed automatic transmission, it could probably restrict the big V8 to two forward gears and nobody would notice. The bottom line is that not only is the new S550 more powerful than its predecessor, it also feels much more refined. Refinement by way of technological advancement certainly fits in with the rest of the S550. Not only is the 550\'s cabin imbued with all the niceties that a luxury car should bring - leather, wood, chrome, etc - but there\'s a virtual smorgasbord of computerised gadgets to relax, coddle and protect you from the elements.