It was just four years ago that Aston Martin introduced the Rapide, and already the British automaker is back with a new and improved version of this sporty four-door. The new model, called the Rapide S, has a bolder look and more muscle under the hood—its 6.0-liter V-12 now makes 550 hp, an increase of 80. This new AM11 engine is mated to a 6-speed Touchtronic 2 ZF automatic transmission with column-mounted sequential shift paddles. The bump in performance is good for sub-5-second acceleration from zero to 60…