Press the start button on the dash and it’s tempting to get out and check the model name on the trunk. This is the 540i, but at startup it makes a distinctly four-cylinder chunky hum. One of the earliest and strongest first impressions a car can make is engine sound at start-up. It’s a less than stellar first impression. But hit the gas and you know it’s the six. Just set the Driving Dynamics Control Switch to sport and leadfoot it. A deeper, muscular sound rushes its way from the dual tailpipes, and shifts snap off in quick succession. It moves, quickly. BMW tuned this exhaust with two characters -- hearing both of them helps you understand the car’s two personalities.