Mercedes-Benz SLR McLaren -- The Technology

Press Release

Mercedes-Benz SLR McLaren -- The Technology

In detail:

Engine and transmission:
V8 powerplant with motor racing in its genes

• High-tech powerplant with 780-Nm torque
• Metal catalytic converters for low exhaust gas emissions in line with EU 4 standard
• Sidepipes reminiscent of 1950s SLR models
• 5-speed automatic transmission with 3-stage manual shift program

An abundance of power and high-tech features from the world of motorsport – these are the defining characteristics of the V8 engine in the Mercedes-Benz SLR McLaren. Which means that the first eight-cylinder to be completely developed by Mercedes-AMG fits perfectly into the high-performance concept of the new Gran Turismo. When developing the powerplant, the AMG engineers applied both the expertise they had acquired during their three-decade involvement in motorsport and the stringent standards of the Mercedes-Benz brand. After an extensive concept phase, they decided in favour of an eight-cylinder design with a 5.5-litre displacement, a cylinder angle of 90 degrees, a screw-type compressor and a crankshaft supported by five bearings. The result is impressive: from a mere 1500 rpm, the SLR powerplant delivers torque of over 600 Nm, rising to 700 Nm at 2000 rpm. The maximum of 780 Nm is available from 3250 rpm and remains constant in a broad engine speed range up to 5000 rpm. The supreme torque curve, coupled with the agile response of a sporty engine which never denies its high-performance character (it offers a peak output of 460 kW/626 hp at 6500 rpm – an extraordinarily high engine speed for this displacement size) speak a powerful language. As the figures indicate, the new SLR is endowed with what is currently one of the most powerful engines to be found in a series-produced roadgoing sports car. An overview of the key data:
With this much power under the bonnet, the Mercedes-Benz SLR McLaren's performance figures are among the best in its class:
Fuel consumption is 19.1 mpg (NEDC combined consumption, provisional figure).

Power from screw-type compressor

To ensure good cylinder charging, the engine has a mechanical compressor with two screw-type aluminium rotors which, in the interests of low friction losses, are Teflon-coated. The charger is so compact that the engine specialists were able to install it between the two cylinder banks of the V8 powerplant. Despite the space-saving design, its innovative technology allows a significantly higher charge pressure than conventional mechanical chargers because the two rotors achieve a top speed of around 23,000 revs per minute, forcing air into the air inlet of the 5.5-litre powerplant at a maximum pressure of 0.9 bar. This means that they compress around 1850 kg of air into the eight combustion chambers per hour – which is up to 30 per cent more than the figure achieved by rival charging systems. In order to ensure the greatest possible efficiency, the AMG engineers created an intelligent engine management system which regulates the operation of the screw-type compressor according to the engine speed and load. This means that the charger is only active when it is needed. Nevertheless, the system ensures that the maximum output is available as soon as the driver calls it up by stepping on the accelerator. When this occurs, the electronics of the engine management system trigger an electromagnetic coupling which immediately activates the compressor, which is powered by a separate poly-V-belt. Because the charger delivers its output in fractions of a second, even the most perceptive driver will not notice the phases without charger support. The charger system's air recirculation flap, opened under partial load, helps reduce fuel consumption.

Two charge-air coolers with separate water circuit

In addition to the compressor, the electronics also monitor all other variables relevant to the engine – both the powertrain management for the pedal-dependent drive characteristics and the implementation of spontaneous transmission or ESP® interventions. They also ensure optimum control of the water circuit for the charge-air cooling system, as efficient charge-air cooling is essential where high output is concerned. This is because cold air is denser than warm and also contains significantly more oxygen for combustion. In the Mercedes-Benz SLR McLaren's V8 engine, two separate charge-air coolers are responsible for this key task – one per cylinder. This ensures that loss of pressure is very low.
Click photo for larger size The highly effective engine-based charge-air coolers operate along the lines of an air/water heat exchanger: the air, compressed and hence warmed by the compressor, is cooled via a separate water circuit – making the process independent of the temperature outside. This means that the eight-cylinder can deliver its maximum output and torque spontaneously at any time. The high performance figures of the eight-cylinder engine in the new SLR, however, not only demand good cooling of the combustion air but also result in an overall increase in engine cooling requirements. The engineers met this need by incorporating generous cooling air inlets and outlets and a powerful 850 watt suction-type fan.