Mercedes-Benz SLK55 AMG and Audi TT RS: Two Ways to Skin a Set of Tires With addictive doses of power and handling, the Mercedes-Benz SLK55 AMG and Audi TT RS have become legitimate contenders to the supremacy of sports cars like the Chevrolet Corvette and Porsche Boxster S. But these special-edition German rockets, roughly co-equals, take wildly divergent routes to producing sound and fury, as I recently learned during back-to-back drives with the pair. And the car chosen says a lot about the performance values of the buyer. The Mercedes is pure malevolence beneath its extroverted skin. Naturally, the Benz selects a skull-crushing V-8 from the weapons rack, a hand-built 5.5-liter unit, the only naturally aspirated motor in the bi-turbo-obsessed AMG line-up. The result is 415 free-breathing horsepower enlisted to move a pretty little two-seater. This is the kind of ridiculous cognitive dissonance that AMG favors (count me in), along with a savage exhaust note whose volume is permanently dialed to 11. Prod the gas and the Mercedes slobbers and howls like the Tasmanian Devil as it tornadoes to 60 miles per hour in a manufacturer-estimated 4.5 seconds, and to an uncapped 174 m.p.h. top speed when equipped with the optional AMG handling package. Unequipped, top speed is limited to 155 m.p.h. Optional black alloy AMG wheels against a white body, along with carbon fiber trim, made clear that my test model was no boulevardier. And the brand's overtures toward fuel efficiency are more than just obliging nods, with a Formula One-derived engine stop-start system that reportedly bolsters fuel economy by nearly 30 percent over the last-generation SLK55, to an estimated 19 miles per gallon in city driving and 28 m.p.g. in highway driving, despite a gain of 60 horsepower. In repose, the Audi is as subtle as the Mercedes is flashy. It's just another bubble-canopied TT coupe, albeit with fat 19-inch wheels and a rear spoiler. On paper or at the curb, the Audi looks like it wouldn't stand a chance against the SLK55. Ah, but this is a rare TT, one of very few cars Audi has exported to America to wear an RS badge, denoting the top rank of Audi performance. Audi's own claim to craziness is the 360 horsepower wrung from a mere five cylinders and 2.5 liters of displacement. To accomplish this, Audi turbocharges the engine to within a square inch of its life, with a huge 17.4 p.s.i. of turbo boost. With its welcome 6-speed manual shifter and Quattro all-wheel-drive powering four wheels, the TT RS scampered to 60 m.p.h. in 4 seconds flat in a test by Car and Driver. For some perspective, that's faster than Audi's $100,000-plus R8. With less than half the displacement of the SLK55 and three fewer cylinders, the Audi emits a throbbing techno soundtrack to the Mercedes" Marshall-stack thunder. The Audi's song is spiky and synthetic, yet compelling: a digitally sampled fighter jet filtered through the titanium sport exhaust. The Audi, at $57,725 to start, also costs nearly $11,000 less than the SLK55, at $68,375. As for class benchmarks like the Boxster S and Boxster Spyder, those models still offer the purest connection between car and driver. But on public roads, purity isn't everything, and the Audi or Mercedes would slap the Porsches silly, with equal grip in corners but far more urge at any point in the power band. Whether those impressions would hold against the 2013 Boxster remains to be seen. For Audi and Mercedes, whose previous efforts to engineer brawn into these models often got them dismissed as luxury poseurs, the equally lusty sound effects produced by these revitalized machines should be music to the ears of enthusiasts everywhere.