Wedged under the 2006 Audi RS 4’s hood is a 420-horsepower V8 engine equipped with direct fuel injection. Able to rev to 8,250 rpm, this 4.2-liter powerplant makes 90 percent of its maximum 317 lb.-ft. of torque between 2,250 and 7,600 rpm, promising an astoundingly flat powerband with plentiful response throughout the rev range.