The new Mercedes-AMG SL: engine, transmission and all-wheel drive

Oct 28, 2021

At market launch, the new roadster starts with two output levels of the AMG 4.0-litre V8 biturbo engine. And for the first time in its history, the SL also transfers the power to the road with all-wheel drive.

In the top model SL 63 4MATIC+ (combined fuel consumption 13.0-12.5 l/100 km, combined CO2 emissions 294-282 g/km) the engine develops 430 kW (585 hp) and provides a maximum torque of 800 Nm over a wide rev range from 2500 to 4500 rpm. The roadster's top engine thus conveys effortless superiority in every rev range. The acceleration from 0 to 100 km/h in 3.6 seconds illustrates this, as does the top speed of 315 km/h. In the Mercedes-AMG SL 55 4MATIC+ (combined fuel consumption 13.0-12.2 l/100 km, combined CO2 emissions 294-277 g/km), the V8 engine delivers 350 kW (476 hp) and a peak torque of 700 Nm. The sprint from standstill to 100 km/h takes 3.9 seconds, the top speed is 295 km/h.

The further developed AMG 4.0-litre V8 engine still operates with biturbo charging, in which the two turbochargers are not located on the outside of the cylinder banks, but in between them in the cylinder-V. The advantages of the "hot inside V": a compact engine design, spontaneous response of the turbochargers and low exhaust emissions thanks to optimal airflow to the close-coupled catalysts.

To further improve response, turbochargers with twin-scroll technology are used. Here, the housing of the turbocharger is divided into two parallel flow channels. Combined with two separate exhaust ducts in the exhaust manifold, this makes it possible to control the exhaust gases on the turbine wheel separately. One duct is fed by the exhaust gases of the first and second cylinders of a cylinder bank, the other by the exhaust gases of the third and fourth cylinders. The aim is to prevent the individual cylinders from having mutually adverse effects on the gas cycle. This reduces the exhaust gas back-pressure and improves the gas exchange. The results are increased output owing to improved cylinder charging with fresh mixture, more torque at low revs and immediate response times.

Engine features also include weight-optimised pistons, an adapted air intake and intercooling system, as well as extensive software developments. The jet-guided direct petrol injection with piezo injectors, the all-aluminium crankcase, the 4-valve technology with camshaft adjustment, the air-to-water intercoolers, the alternator management, the ECO start/stop function and the gliding mode have been retained.

Special modifications for use in the SL

For use in the SL, the internally named M 177 engine received a new oil pan, repositioned intercoolers and active crankcase ventilation. The intake and exhaust ducts have been optimised for even more effective gas exchange and the exhaust gas routing for the catalytic converter box and petrol particulate filter has been enlarged. The developers achieved the increased output of the SL 63 4MATIC+ primarily through higher boost pressure and greater air flow, as well as modified engine software. To sum up, the eight-cylinder engine thrills with its exceptional power delivery and powerful acceleration in all engine speed ranges combined with maximum efficiency for low consumption and emission values.

In the SL 63 4MATIC+, the eight-cylinder engine features active engine mounts. The SL 55 4MATIC+ can be optionally equipped with this as part of the AMG DYNAMIC PLUS Package. The mounts solve the conflicting goals of achieving as soft a connection as possible to the powertrain for high comfort and as rigid a connection as possible for optimum driving dynamics, by steplessly and quickly adapting their rigidity to the respective driving conditions. These are liquid-filled rubber mounts. The vehicle sensors detect the respective driving situation as well as the resulting vibration behaviour of the engine and pass this information on to a control unit. It regulates the force with which the engine is coupled to the body and thus optimises the handling. For this purpose, a magnetic damper fluid is pressed through an annular gap of a coil in the mount. Differently high currents generate a magnetic force that regulates the flow and thus the engine mounts according to the information from the control unit.

Three cooling circuits for optimal thermal management

To ensure that the new Mercedes-AMG SL doesn't get too hot even when it's being pushed to the limit on race tracks, three cooling circuits are used to maintain an even temperature. The high-temperature circuit cools the AMG 4.0-litre V8 biturbo engine and the two exhaust gas turbochargers. It also supplies the heating heat exchanger for on-demand and comfortable temperature control of the interior. The mechanical water pump is positioned on the engine block to save space and is driven reliably and directly by the timing assembly, with a pinion on the camshaft meshing with the water pump gear. The pump circulates a total of 12.3 litres of coolant at up to four bar pressure and 400 litres per minute.

The three-tier main cooling module (high-temperature radiator, low-temperature radiator, condenser), the flange-mounted intake fan and the auxiliary intake radiator (for the high-temperature circuit) - which is installed "horizontally" for a low centre of gravity, among other things - are positioned centrally in front of the engine behind the large radiator shroud. This means that they can be optimally supplied with a large volume of air. Thermal management is influenced not only by the three-stage thermostat and the shut-off valve (when the engine is cold, the cooling circuit is stopped so that the engine comes up to operating temperature more quickly), but also by active aerodynamic elements such as the two AIRPANELS in front of the main cooling module or the active aerodynamic element in the front underbody.

With a volume of 7.2 litres, the low-temperature circuit is somewhat smaller. It serves the intercoolers, the AMG SPEEDSHIFT MCT 9G transmission and the engine control unit. The performance of the main radiator is supported by an auxiliary radiator in the left wheel arch. Indirect air-to-water intercooling has enabled the developers to ensure efficient charge air cooling for high performance even in difficult ambient conditions. The plastic air intake box is designed to allow maximal equal distribution of air across the pipes - with minimum pressure loss. The dimensioning of the charge air cooling components allows the charge air temperature to be kept at precisely defined values above the ambient temperature.

The third cooling circuit is responsible for the engine oil. The oil-to-water heat exchanger ("oil cooler") in the right wheel arch enables rapid heating of the oil. This has a positive effect on the service life of the engine and reduces consumption after a cold start. In addition, this circuit prevents the engine from overheating and thus being damaged. The external oil cooler is controlled by its own oil thermostat. The oil and water pipes are made of aluminium instead of steel, which helps to reduce weight.

Digital and smart assembly by hand: "One Man, One Engine"

The engine is assembled purely by hand. In the AMG engine factory at the Affalterbach site, the "One Man, One Engine" principle is combined with Industry 4.0 manufacturing methods. This is designed according to modern knowledge of ergonomics, flow of goods, quality assurance, sustainability and efficiency. Smart production is characterised by maximum flexibility, is transparent and highly efficient. It assures and improves the quality of the engines and production processes using digital technologies.

Short shift times, high efficiency: the AMG SPEEDSHIFT MCT 9G transmission

The AMG SPEEDSHIFT MCT 9G transmission (MCT = Multi-Clutch Transmission) is specially adapted to the requirements of the new SL. A wet start-off clutch replaces the torque converter. It reduces weight and, thanks to its lower inertia, optimises response to accelerator pedal commands, especially during spurts and load changes. The elaborately calibrated software ensures extremely short shift times and, if required, fast multiple downshifts and, thanks to the throttle blip function in the "Sport" and "Sport+" driving modes, delivers a particularly emotionally appealing gearshift experience. Here, defined ignition adjustments enable even faster gearshifts than in the other modes. In all modes moving off occurs in first gear in order to always guarantee a dynamic driving experience. There is also the RACE START function which ensures optimal acceleration from a standstill.

The highlights of the transmission include:

  • Adaptation of the shift characteristics to the selected AMG DYNAMIC SELECT driving mode
  • In manual mode "M", the transmission responds immediately and precisely to manual gearshift commands from the driver and implements the commands at lightning speed.
  • The temporary M mode allows an immediate change to manual mode "M" – merely by using the paddle shifters
  • Automatic throttle blipping function when downshifting: This effect is automatically active in the "Sport", "Sport+" and "RACE" driving modes (standard on the SL 63 4MATIC+).
  • ECO start/stop function is automatically active in the "Comfort" driving mode.
  • The "gliding" mode can be activated in the "Individual" driving mode.

Fully variable AMG Performance 4MATIC+ all-wheel drive

For the first time in its almost 70-year history, the SL is available with a drive system acting on all four wheels. The two V8 models are equipped with AMG Performance 4MATIC+ fully variable all-wheel drive as standard. This intelligent system combines the advantages of different drive concepts: the fully variable torque distribution to the front and rear axles ensures optimal traction right up to the physical limit. The driver is also able to rely on high handling stability and a high level of safety under all conditions: in the dry, in the wet or in snow. The transition from rear-wheel to all-wheel drive and vice versa takes place continuously on the basis of a sophisticated matrix that integrates the intelligent control into the entire vehicle systems architecture.

An electromechanically controlled clutch connects the permanently driven rear axle variably to the front axle. The best possible torque split is continuously computed according to the driving conditions and driver's input. This means that the new roadster can be driven continuously variably from traction-oriented all-wheel drive to pure rear-wheel drive. Alongside traction and lateral dynamics, the all-wheel drive also improves the longitudinal dynamics for even more powerful acceleration.

Performance hybrids with exclusive AMG concept

At a later date, Mercedes-AMG will also offer the SL with a powerful Performance hybrid drive. The AMG E PERFORMANCE drive strategy is based on the guiding principle of offering an electrified powertrain that further enhances driving dynamics while also being highly efficient. With the increase in performance due to the additional electric motor, the development team was also able to improve the efficiency of the entire vehicle in parallel - and achieve lower emissions as well as lower consumption.