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The high-performance version of the redesigned second generation of the Mercedes CLS-class four-door retains the numerical name of its predecessor but not the normally aspirated 6.3-liter V8 those digits represented.

Under the hood sits a 5.5-liter version of the new 4.6-liter biturbo V8 of the Mercedes CLS550. Although this new AMG powerplant gives up nearly a liter of displacement to its predecessor, it more than makes up for the difference thanks to twin turbos--one per each bank of cylinders running on 14.5 pounds of boost. The engine pumps out 518 hp and 516 lb-ft of torque versus the 6.3-liter's 507 hp and 465 lb-ft of torque. An optional AMG Performance package increases boost to 18.8 pounds for 550 horses and 590 lb-ft of torque.

Getting this power to the rear wheels is the AMG seven-speed multiclutch transmission with four modes--comfort, sport, sport and manual. A Race Start launch mode is part of the Performance package option.

While the CLS550 rides on the Airmatic suspension, the CLS63 AMG has an adaptive suspension with driver-adjustable settings.

Staggered 19-inch wheels and massive 14.2-inch brake discs at all four corners are also part of the AMG upgrade.

By PATRICK C. PATERNIE on 5/19/2011 in autoweek.com