The older AMG 6.3 liter V8 (which made its debut in 2005) naturally aspirated engine has a displacement of 6,208 cc, compared to the 5,461 cc of the new V8. For the first time, AMG is also utilizing the advantages of gasoline direct injection with spray-guided combustion and piezo-electric injectors: thanks to its higher thermodynamic efficiency, this technology makes more efficient use of fuel and leads to lower exhaust emissions. AMG combines this spray-guided combustion with twin turbochargers. Other highlights include an all-aluminum crankcase, four-valve technology with adjustable camshafts, an air/water intercooler, generator management and the standard stop-start function.

The AMG 5.5-liter V8 biturbo engine develops a peak output of 400 kW (544 hp) and maximum torque of 800 N·m (590 lb-ft). In conjunction with the AMG Performance package these figures are increased to 420 kW and 900 N·m. The major difference between the two performance classes is an increase in the maximum charge pressure from 1.0 to 1.3 bar.

With the provisional NEDC fuel consumption of 10.5 L/100km, the new S 63 AMG is 3.9 liters more economical than the preceding model powered by the naturally aspirated AMG 6.3-litre V8—despite an increase in output by 14 kW (19 hp) and 34 kW (46 hp) and in torque by 170 and 270 N·m for the base and performance package engines respectively. CO₂ emissions have likewise been significantly reduced: at 246 grams per kilometer, the figure is 28.5% lower than for the previous model.

Taking into account the enormous performance and torque figures, the new AMG 5.5 liter V8 biturbo engine is in parts relatively twice as efficient as many mid-segment or compact-class diesel engines, according to AMG. The 5.5L V8 has a weight/power ratio of 0.41 kg/hp for the basic engine, and 0.39 kg/hp with the AMG Performance package.

The high-performance sedan accelerates from zero to 100 km/h in 4.5 seconds, and has an electronically limited top speed of 250 km/h (155 mph). The 100 km/h mark is reached in 4.4 seconds with the AMG Performance package, with the top speed increased to an electronically limited 300 km/h (186 mph).

The flat torque curve ensures enormous pulling power in all speed ranges: 670 N·m are already available at 1500 rpm, and the maximum torque of 800 N·m is delivered 500 rpm later, remaining constant to 4500 rpm. With the AMG Performance package, the engine delivers 875 N·m of torque at 2000 rpm, with a constant 900 N·m available between 2500 and 3750 rpm.

MCT 7-speed sports transmission with Controlled Efficiency mode and stop-start function. Power is transferred by the AMG Speedshift MCT 7-speed sports transmission used exclusively by AMG. The wet start-up clutch replaces a conventional torque converter, and helps to save fuel. The improved fuel economy is also in large measure due to the standard stop-start function. This system is active in the transmission’s Controlled Efficiency (“C”) mode, and switches the eight-cylinder engine off when the car comes to a stop. In C mode the sports sedan always starts off in second gear, and the transmission shifts to the next, higher gears at an early stage. With its high torque at low engine speeds, the V8 engine encourages a smooth, effortless driving style.

The eight-cylinder biturbo engine also features the generator management system from the E 63 AMG: whenever the engine is on the overrun or when braking, kinetic energy is used to charge the battery rather than being wasted as heat in the usual way. In all other operating modes a combination of onboard network and generator management enables the generator to be kept at a low voltage. This reduces the load on the engine and makes for fuel savings of around 0.15 liters per 100 kilometers according to the NEDC standard, and up to 0.2 L/100 km in city traffic with its frequent overrun and braking phases.