The SL suffix always has been a bit optimistic, even when applied to the original Mercedes-Benz SL roadster of 1957. Although the car was definitely sporty, it wasn't exactly light, tipping the scales at a relatively well-fed 2926 pounds. With each successive generation, Stuttgart's SL has turned into a Serious Leviathan. The latest and--literally--greatest iteration is the line's new flagship, the SL55 AMG. It weighs a sumoesque 4311 pounds--143 more than the already hefty SL500. Mercedes and its in-house tuner AMG have more than compensated for this portliness, however, with a sensational V-8 engine that answers all questions and quashes all doubts. Wedging a belt-driven, screw-type supercharger between the cylinder banks of AMG's all-aluminum, SOHC 5.5-liter V-8 adds 167 horses to the SL corral, for a total of 469. The result is a true thoroughbred, a serious rival for the Porsche 911 Turbo, the Aston Martin V12 Vanquish, and the Ferrari 360 Modena.
Visually, the AMG version of the fifth-generation SL is no improvement over the SL500. The various spoilers, the chiseled rocker covers, and the F1-inspired nose seem to neutralize the SL's stealthy appeal. The cockpit is swathed in soft leather and even softer suede, and it's nicely decorated with brushed aluminum accents. We aren't fond of the gauges, however, which are difficult to read.
The SL55 AMG is the first Mercedes-Benz model to be fitted with a push-button manu-matic transmission, and it shows. Before you can use the steering-wheel-mounted controls, you have to push a button on the center console to engage the manual mode. Even then, the AMG solution isn't as convenient or fail-safe as Porsche's Tiptronic system, because the left-hand button performs only downshifts, and the right-hand one performs only upshifts. That's fine, as long as the road is reasonably straight, but it can be confusing once you start winding on lock. The SL55 AMG also suffers in some other respects: It guzzles fuel, it follows the road surface like a truffle pig, and it has a lot of trouble putting down its prodigious power in the wet.
But these are minor quibbles, because the SL55 AMG is a fabulous device. Spinning at up to 23,000 rpm, the supercharger's blades hum like angry hornets. Unleashed, the mighty engine presses your torso firmly into the seat. Since the top-of-the-line SL takes just 4.7 seconds to reach 62 mph, your eyes are well advised to blink less and open wider. Unless you have taken a handful of bravery pills, it's best to wait awhile before switching off the stability control, because this engine lays on more muscle than a pair of nervous arms can easily master. At a leisurely 2650 rpm, the V-8 whips up an astounding 516 pound-feet of torque, for which AMG's engineers had to reinforce the driveline and rear suspension. Bravery up and stability control off, power oversteer is just a stab of the throttle away.
The blower adds so much extra spice to the 24-valve V-8 that AMG felt compelled to introduce a new option for Europe: a $1500 chip that bypasses the speed governor and raises the limit from 155 to 186 mph. Completely unrestricted, the awesome retractable-hard-top roadster could theoretically top 203 mph, but there aren't any road tires for the car that can withstand that kind of load and speed.
You don't need to be a hero to get the best out of the SL55. It performs with rare effortlessness, understated urge, and spectacular low- to midrange punch. The five-speed gearbox is quick, attentive, smooth, and seemingly gifted with foresight, so there's really no need to use the manual-shift feature.
With the help of Active Body Control, a low center of gravity, and a set of wide eighteen-inch tires, this car almost defies physics. There seem to be a nearly endless supply of grip and a rare ability to shrug off the vagaries of the road. Add the instant-on response of the electrohydraulic braking system and the engine's addictive thrust, and you can understand why this is one of the most entertaining means of getting from point A to point B. The only dynamic disappointment is the SL55's steering, which doesn't feel as lithe and spontaneous as that of the lighter-weight SL500.
This fastest-ever street-legal production Mercedes-Benz starts at about $96,000. That's a lot of money for an SL but a fair price for what is one of the most versatile and user-friendly of hard-core sports cars. And it will be rare, too: Mercedes plans to sell only 4000 SL55 AMGs a year worldwide.