Mercedes-Benz SLR McLaren-Part one
Top-class technology for 21st-century Gran Turismo
Mercedes-Benz SLR McLaren: top-class technology for 21st-century Gran Turismo
- High-torque V8 compressor engine with 460-kW/626-hp output
- 0 to 100 km/h in 3.8 seconds
- World's first series-produced car to have carbon fibre front crash structure
- High-performance brake discs made from fibre-reinforced ceramic
Engine and transmission: V8 powerplant with motor racing in its genes
- High-tech powerplant with 780-Newtonmetre 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 8-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 8-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 Newtonmetres, rising to 700 Newtonmetres at 2000 rpm. The maximum of 780 Newtonmetres 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:
Cylinder arrangement
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V8
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Cylinder angle
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90o
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Valves per cylinder
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3
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Displacement
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5439 cc
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Bore/stroke
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97.0/92.0 mm
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Cylinder spacing
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106 mm
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Compression ratio
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8.8 : 1
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Output
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460 kW/ 626 hp at 6500 rpm
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Max. torque
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780 Nm at 3250-5000 rpm
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Engine weight
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232 kg
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Power/weight ratio
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1.9 kW/kg
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With this much power under the bonnet, the Mercedes-Benz SLR McLaren's performance figures are among the best in its class:
0–100 km/h
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3.8 s*
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0–200 km/h
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10.6 s*
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0–300 km/h
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28.8 s*
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Top speed
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334 km/h*
| *provisional figures
Fuel consumption is 14.8 litres per 100 kilometres (NEDC combined consump-tion, 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 kilograms of air into the eight combustion chambers per hour – which is up to 30 percent 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 de-livers 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 con-tains 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.
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 8-cylinder can deliver its maxi-mum output and torque spontaneously at any time. The high performance figures of the 8-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.
Crankcase with dry sump lubrication
The Mercedes-AMG GmbH engineers also applied their extensive experience in the world of motorsport and in the design of high-performance engines to other details of the SLR powerplant. The entire engine housing, for example, and the lower section of the closed crankcase are cast in aluminium. Each crankshaft is finely balanced and is supported by five bearings made from durable plastic, allowing long-term transfer of the impressive forces from the compressor engine.
The pistons are forged and are therefore only manufactured in minimal numbers. Like the forged lightweight conrods, they are precisely measured and weighed and allocated to the individual engines in such a way as to produce minimal balancing tolerances. The pistons move in highly robust, wear-resistant and friction-optimised walls made from a special compound which is otherwise only used in motor racing. Dual oil injection effectively cools the pistons.
The design of the powerplant's oil cooling system is also based on experience gathered in the world of motor racing: a sophisticated dry sump lubrication system with an oil capacity of around eleven litres, combined with a five-stage oil suction pump and a two-stage oil pressure pump, ensures reliable lubrication under all on-road conditions. An important side effect of this technology is that, because of the dry sump lubrication, usually only used in motor racing vehicles, the engine is less tall and can therefore be installed at a lower level, allowing a low centre of gravity which benefits dynamic handling.
Following the usual practice at Mercedes-AMG, each SLR engine is manufactured by hand. In order to achieve the highest quality, the principle of 'one man, one engine' is applied. This means that each powerplant is the responsibility of one AMG engineer, who carries out the entire engine assembly process – from installing the crankshaft in the engine block and assembling the camshafts and the compressor to cabling.
Powerful high-pressure pumps in the tanks
The SLR's high-performance engine draws its fuel from two interconnected aluminium tanks. They are installed at a relatively low level to the left and right of the rear axle in order to keep the centre of gravity as low as possible to further en-hance dynamic handling. The tanks, which have an overall capacity of 97.6 litres – of which twelve litres form the reserve – are equipped with two integral high-pressure fuel pumps. These are controlled by the engine management system and ensure that the fuel supply matches the engine speed and load. Here too a highly effective, SLR-specific solution was developed: one pump operates constantly while the second is only activated as required.
Four metal catalytic converters for efficient emission control
Where the engine is concerned, secondary air injection and dual ignition create the criteria required for low exhaust gas emissions. A sophisticated exhaust gas system complements these measures: the cascade-design twin-pipe system consists on both sides of a bulkhead-mounted catalytic converter and a main catalytic converter with a special noble metal coating, accommodated in the same housing. The state-of-the-art metal design allows extremely thin wall thicknesses and therefore a very low exhaust gas backpressure. Thanks to its cutting-edge technology of its engine management and emission control systems, the new SLR's 8-cylinder engine already meets the stringent exhaust gas limits stipulated by EU 4 plus the current US limits.
On each side of the vehicle the catalytic converter housing opens into a rear silencer which, just behind the front wheels, flows into two stainless steel pipes with a diameter of 60 millimetres. These sidepipes – a further reminder of the 1950s SLR racers – allow the smooth-surfaced underbody, which plays a crucial role in producing the new Mercedes-Benz SLR McLaren's first-class aerodynamic properties. The silencers are folded several times in precisely calculated acoustic sections which produce the thrilling characteristic engine sound of the Mercedes-Benz SLR McLaren. The capacity of each silencer is 19.6 litres.
Manual transmission program for racing car-style shift times
The five-speed automatic transmission, developed by Mercedes-Benz and already successfully used in several exceptionally powerful models, is also designed for high performance. It has been specially optimised for very high torque and also offers the driver the option of choosing between different shift characteristics. The transmission transmits the engine power via a finely balanced aluminium and steel powertrain to the differential and the rear axle.
The Speedshift system, developed by Mercedes-AMG for particularly sporty driving, offers even more functions in the new SLR. The driver can decide, for example, whether to leave the shift work to the automatic transmission or to shift gears manually. He or she can also select the shift speed, determining how sporty the gearshifts are. A rotary switch in the centre console offers a choice of three settings: "Manual", "Comfort" and "Sport". The activated programme is indicated in the instrument cluster display by the letters "M", "C" or "S".
"Comfort" and "Sport" are automatic shift programs which, as the names indicate, place the emphasis either on comfort or on a more sporty drive. In "Manual" mode, on the other hand, the driver can select the five gears either using the but-tons on the steering wheel or using the Touchshift function on the selector lever. When "Manual" is selected, he or she also has the option of choosing between three shift stages for a sportier driving style:
In the sequence indicated here, the response, reaction and closing times of the couplings in the automatic transmission, and hence the shift processes themselves, become increasingly shorter.
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