The Mercedes-Benz SLS AMG made its first public appearance at the Frankfurt show in September, 2009. It mixes vaguely retro styling — recalling the 300SL gullwing of 1954 — with contemporary engineering that places the new car on the top floor of the sportscar hierarchy. It’s also the first car developed autonomously by Daimler’s prestige sporting division AMG.
History will not find the 2010 gullwing lacking in technology or road performance. The combination of a lightweight space-frame structure, double wishbone suspension and a drivetrain that delivers 571PS through a seven-speed twin-clutch transaxle will make sure of that. There’s also the small matter of the gullwing doors.
Mercedes-Benz SLS AMG.
The SLS’s 1620kg kerb mass is distributed pretty much perfectly for a rear-wheel drive car, with 53 per cent. over the rear wheels. Any closer to 50/50 and understeer becomes inherent. AMG’s 6.2-litre atmospheric V8, designated M159, is mounted in a front-mid position, behind the front axle line. It drives a rear-mounted transaxle by way of a carbon-fibre propshaft running in a rigid torque-tube that connects the housings of the engine and transaxle. This arrangement — a front engine with a rear-mounted gearbox — gives a higher polar moment of inertia than a mid-mounted engine with the gearbox underneath or behind, making the car less manoeuvrable in extremis but more stable in a straight line and in fast open bends.
A multi-disc locking differential is incorporated in the transmission housing and works in conjunction with the car’s ESP (electronic stability program). The latter applies the brakes to a driving wheel that’s beginning to lose traction. There are three ESP modes — on, sport and off — though it seems that even ‘off’ isn’t really off.
Mercedes-Benz SLS AMG drivetrain. Click here for a larger version (118k).
AMG’s V8 uses dry sump lubrication. This allows lower mounting of the engine and more reliable lubrication under extreme cornering loads. The AMG dry-sump system uses vacuum and pressure pumps: the former draws oil from the tank, the latter delivers it at a predetermined pressure to the engine.
Oil pressure is controlled according to demand as an efficiency measure; the charging of the battery is likewise ‘managed’, with the generator switched out when the engine is under load. Kinetic energy capture operates to charge the battery during overrun and braking.
The GT3 is the racing derivative of the SLS. It was conceived (as you might imagine) for homologation according to the FIA’s GT3 rules, which specify that a car must be ‘near-series’; in practice, this means that you leave the engine alone and go to town on everything else.
AMG’s main focus when modifying the body of the SLS was on aerodynamic performance. There’s a new front apron with larger air intakes: a wide aperture below the grill, and a wing-shaped transverse fin to supply air to the engine oil cooler and brake discs. The two air intakes below the headlights have the same function. The bonnet has a central cooling air vent. The wheel-arches contain air-vents and the side-skirts have ducts to grab air for cooling the rear brakes. The underbody is smooth, there is a rear diffuser of course, and the carbon-fibre rear aerofoil has multiple adjustments for racing. The aim, as always, is to create maximum downforce while keeping the drag coefficient as low as possible, which is a direct tradeoff.
Mercedes-Benz SLS AMG GT3.
The front and rear wings are wider than those of the standard car to make space for the large racing tyres. At 1990mm, the body of a GT3 is 51mm wider than that of a ‘normal‘ SLS.
Downforce at the front axle is provided by four externally mounted ‘flics’ and the carbon-fibre front splitter: this blends into the smooth underbody cladding which ends with the rear diffuser.
Hot air from the engine compartment is vented into the wheel arches from vents in the inner wings.
Lightweight polycarbonate is used to glaze the side and rear windows; the owner can also opt for a polycarbonate windscreen.
Holomologation by the FIA will see the Federation determine the maximum output of the AMG 6.2-litre V8 on the ‘balance of performance’ principle, to ensure that all the racing cars taking part in an event have an equal chance of success. Kerb mass is also determined.
Power transmission in the SLS GT3 is by means of a sequential six-speed racing gearbox with steering wheel shift paddles, rather than the twin-clutch seven-speed unit used on the road car.
All four wheels are located by double wishbones of forged aluminium. Adjustment is provided to allow a car to be set up for the race-track: the springs and dampers, suspension height, the anti-roll bars, track width and camber can all be adjusted. The rack-and-pinion steering has a more direct ratio than the standard car,
and speed-sensitive power assistance is fitted. The wheels are centrally-locked AMG items. Behind them is a composite steel racing braking system with racing ABS.
The cast-iron brake discs are mounted on an aluminium bowl via stainless steel connections in a radially and axially floating arrangement. This arrangement is aimed at providing good heat conduction and therefore fade-resistance. The front calipers are fixed and have six-pistons; four-piston fixed calipers are used at the rear.
For space reasons, AMG’s ceramic composite braking system that’s offered as an option for the standard car is not compatible with the 18-inch wheels prescribed by the FIA rule-book.
Wheel sizes are 12x18 inches at the front and 13x18 inches behind, for racing tyres of 287x682mm (front) and 315x708mm (rear). Slicks, intermediates or rain tyres can be used. Pit-stops and wheel-changes are assisted by a pneumatic jacking system integrated into the underbody: four pneumatic jacks lift the GT3 by around 190mm to allow very rapid wheel-changes by the pit crew.
The GT3 adds a steel rollcage to the aluminium spaceframe. Quite apart from providing protection for the driver in an accident, this improves the torsional stiffness of the bodyshell, and thus handling precision.
Inside, a central display in place of conventional dials provides the driver with reading material for those long straights.
The SLS AMG GT3 will be entitled to take part in all GT3 race series. This includes the 24-hour race in Spa-Francorchamps in Belgium or the Nürburgring.
Order books for the GT3 will open in autumn 2010; deliveries are expected to start in spring 2011.