Both feature a twin-turbo V8 engine driving all four wheels through a seven-speed automatic transmission and 4Matic all-wheel drive, but where the S550's displaces 4.7 liters to produce 449 horsepower and 516 lb-ft of torque, the S63's displaces 5.5 liters and churns out an even more impressive 577 horsepower and 664 lb-ft of torque. That's enough to send a coupe that weighs a hardly featherlike 4,400 pounds to 60 miles per hour in 3.9 seconds and top out at 186 mph.
The hand-built engine is a good 41 hp and 74 lb-ft more capable than the outgoing CL63's, but thanks in part to stop/start engine management, it's more fuel efficient. Meanwhile a retuned air suspension and 20-inch wheels packing available carbon-ceramic brakes keep all that power and pace in check. An upgraded aero kit keeps the wind rushing smoothly around it and makes the S63 look that extra bit more aggressive than the S550 Coupe, while inside the cabin has been refitted with Nappa leather, a three-spoke steering wheel with aluminum shift paddles and more.