The doors of the McLaren 650S Spider open with an upward, outward sweep, a design intended to enable efficient ingress and egress. The theme of ergonomics is carried through to the car’s tidy interior. Indeed, every detail of this $280,225 top-down roadster is well thought out, purposeful, and practical. But when the Start button is pressed, a flurry of emotions sets in.

The twin-turbocharged V-8 fires up and fills the cabin with a deep, mellow boom; the rumble is accentuated by the so-called intake sound g…