With its throaty growl and plentiful power, the Jaguar XK's 4.2-liter, 400-horsepower V8 is the best thing about the car. The blend of refinement, power, and fuel economy (we averaged 22.1 mpg during a week of driving) rivals the best engines from Japan. The transmission is satisfying, too, though the paddle-shifters decided to stop working and Sport mode wouldn't engage halfway through our run up San Diego County's Palomar Mountain. Shutting the car off and restarting it resolved the mystery glitch.