The Audi Coupe GT should have swept America's car enthusiasts off their feet by ... through the standing quarter-mile in 16.6 seconds at 80 mph, with the engine humming contentedly all the while.

The car's rivals, the Audi SQ7 (starts at $90,800) and BMW X7 M60i (starts at $110,900), get about the same. But, they have thirsty turbocharged 4.0- and 4.4-liter V8s under the hood, respectively ...