Mercedes-AMG works its magic on the GLE and GLS's twin-turbo 4.0-liter V-8, upping output from 530 horsepower to 603 horsepower.An active exhaust system broadcasts the V-8's flat-plane-crank sound that is unusual for an SUV.Mercedes-AMG claims a zero-to-60-mph time of 3.6 seconds for the GLE63 S and 3.9 seconds for the GLS63.