First Drive: 2012 Mercedes-Benz SLK55 AMG

When Mercedes handed us the keys to the SLK55 AMG and asked us to drive it to a race track two hours south of the Golden Gate Bridge, we knew we'd be experiencing a certain corkscrew. That corkscrew wound up being the kind used to open bottles of wine at dinner that evening, not the famed corner with the big vertical drop. That we drove the SLK to a race track -- but not on the race track -- is telling.

It's not for a lack of capability, mind you. The SLK55 AMG slings itself to 60 mph in 4.5 seconds, accompanied by the screams of 415 combusting horses racing out of its quad chrome exhaust pipes. Cornering forces are no match for the stiff suspension, which never quite settles down on bumpy roads but refuses to relinquish grip over the worst broken pavement. The oversize brakes easily shave off the 3527-lb SLK's copious speed again and again, and the computer will even grab one of the rear rotors to help rotate the little roadster on turn-in. The steering is well-weighted, accurate, quick and communicative. Dynamically, the SLK leaves very little to be desired. That's not a surprise.

Our surprise was Mercedes' focus on improving fuel economy -- and particularly, the company's unique method of chasing improvements. While the rest of the world, including Mercedes itself, is downsizing and turbocharging, the Swabians engineered a big, new, normally aspirated V-8 for the SLK. This isn't the old three-valve 5.4-liter "55" engine, nor is it a smaller version of the AMG-designed 6.2-liter "63" engine. The SLK55's V-8, code name M152, is a turboless version of the 5.5-liter twin-turbo M157 V-8s we're seeing elsewhere in the Benz lineup. In place of turbos for more power, the 7200-rpm brute uses cylinder deactivation for better fuel economy.

Under light loads between 800 and 3600 rpm and with the convertible roof in place, the V-8 can disable cylinders 2, 3, 5, and 8 by parking those cylinders' valves and cutting spark and fuel. The transition is completely imperceptible save for a telltale indicator on the dash, and the engine can deliver up to 170 lb-ft of torque running on half its cylinders. Bringing all eight cylinders back to life can be accomplished in as little as 30 milliseconds, says Mercedes, and astute drivers will feel the resurrection in the form of a very slight nudge not unlike that of a torque converter unlocking.

They should also notice a difference at the pump. Combined with other fuel-savings measures (like direct injection, automatic start/stop and a hydraulic power steering pump that, according to Mercedes, only uses power when needed), the new SLK55 should deliver considerably improved fuel economy compared with the last SLK55. That is, of course, despite 60 additional hp and with no sacrifice to the throbbing V-8 soundtrack.

With the BMW Z4 no longer chasing after the Porsche Boxster for all-around performance, Mercedes-Benz's little roadster has also been able to relax. That's true of the four-cylinder SLK250 and the V-6 SLK350, and especially so of the V-8 SLK55 AMG. We'd bet good money that the baby AMG roadster would be a riot around a race track, but kudos to Mercedes for acknowledging that it'll probably never happen. No, the focus was on preserving the V-8's acoustic experience and saving some fuel in the process. More miles per gallon means more pocket money for a sumptuous dinner and an exquisite glass of wine after a thrilling, top-down, back-road drive -- which is precisely what SLK55 AMG customers will be looking forward to doing.

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