To some drivers, a special engine can make a car special. An NSX owner will happily tell you his engine has titanium connecting rods. The Corvette ZR1 has a special viewing window built into the hood to help generate conversation. Those driving an SLK55 AMG of the latest vintage might not know it, but the 415-hp V-8 tucked under the roadster’s hood might well be the most special engine in Mercedes-Benz’s lineup.
All Alone in the World
Mercedes puts the AMG stamp on nearly every vehicle in its portfolio. Currently, the “63” AMG cars get a naturally aspirated 6.2-liter V-8 (five models) or a twin-turbo 5.5-liter V-8 (six models). The three “65” AMGs, however few are sold, get a behemoth 6.0-liter V-12 that’s force-fed an air diet by, again, two turbochargers. But the SLK55 AMG stands as the only AMG model with its own engine, a naturally aspirated 5.5-liter V-8 internally known as M152. This torquey V-8 is closely related to the twin-turbo V-8 in those “63” models, but among other differences, this one lacks turbos and runs a higher compression ratio of 12.6:1 versus 10.0:1.
At $68,375, a completely option-free SLK55 AMG carries a $12,700 premium over the V-6 SLK350—the base price also tops those of the Porsche Boxster S and the BMW Z4 sDrive35is. Our test car had another $10,420 in options. Most notable on that list is the $4750 AMG Handling package, which raises the speed limiter to 174 mph (we actually hit 175 in our testing) and includes a limited-slip differential, the AMG Performance suspension, and brake discs upgraded with lightweight aluminum hats. The standard AMG treatment brings front and rear fascias that imply just the right amount of athleticism without drawing too much attention. And a quick-turning (2.2 turns lock-to-lock), small-diameter steering wheel sets off the interior.
As with all AMG V-8s, the SLK’s revs freely and makes haste for its redline (7200 rpm in this case). The accompanying soundtrack, especially with the top down, borders on addictive. Mercedes’ seven-speed automatic shuttles along the power and 398 lb-ft of torque using an AMG-spec clutch pack in place of a torque converter, although in this application, launch control isn’t part of the deal. The new SLK55’s acceleration isn’t so quick that it’ll dethrone the quickest of the AMGs, but it will handily dust anything in its class—the Z4 sDrive35is and the Boxster S are its only real competitors—with a 0-to-60-mph time of 4.1 seconds and a quarter-mile sprint in 12.5 seconds at 116 mph. Both of those measures are 0.2 second quicker than the old SLK55’s.
The SLK’s big brake calipers, clamping on 14.2-inch front rotors and 13.0-inchers out back, work with Continental ContiSportContact 5P tires to stop the car from 70 mph to 0 in 159 feet. Skidpad performance is strong, too, at 0.93 g—a healthy advantage over the 0.88 g of the Z4 35is. AMG-spec 18-inch wheels show off the big brakes.
Sit Down, Gas Up
The seats are plenty comfortable and offer ample support in aggressive driving. The steering is free of dead spots, and turn-in is crisp, although feedback is lacking. The car as a whole seems set up more for touring. It can hang, but hustling the 55 through a sequence of turns requires more work than in, say, a Boxster. Back off a bit, and the car flows elegantly into and out of bends, like a great GT car.
Note to anyone planning a trip in this SLK: The 10-cubic-foot trunk shrinks to six cubes with the top retracted. And when the top is up at freeway speeds, it makes a bit of noise as it flexes.
Despite the direct-injection V-8’s engine stop-start function and cylinder deactivation that kills half of the fire holes, we averaged 18 mpg, 1 mpg below the car’s EPA city rating. Long-distance cruising improved things only slightly: Our best average was 24 mpg—four fewer mpg than the EPA highway number—seen over one tank on a freeway jaunt to northern Michigan. Blame that great engine sound.
You know what’s more special than the engine?
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