Mercedes SLR gets more power
F1-styling and tweaked supercharger
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Mercedes-Benz has pumped up the SLR McLaren with more than 300 modified components for more output, more dynamic chassis tuning, improved aerodynamics and sporty interior appointments.
The new SLR 722 Edition model variant is designed to evoke memories of a particularly special victory achieved in 1955 by the British motor-racing legend Stirling Moss and co-pilot Dennis Jenkinson at Mille Miglia – the classic Italian endurance race – behind the wheel of a Mercedes Benz 300 SLR with start number 722 (denoting the car's start time of 7.22 a.m.).
Merc's new limited-edition series – only 150 models are being produced -- boasts an output of 650bhp, up from the standard car's 617bhp and is for the most part handcrafted at McLaren's Formula 1 works in Woking. MB described the 722 as "the brand's response to calls from highly discerning SLR customers for even more sportiness combined with the same high level of everyday practicality".
The 722 Edition houses the same 5.5-litre supercharged V8 as the standard car. It's assembled by hand at the Mercedes-AMG engine workshops in Affalterbach, Germany, based on the "One man, one engine" principle.
Crankcase
The powerplant's entire engine block with its enclosed crankcase sump is made from cast aluminium. Each crankshaft is precision-weighted and revolves in five bearings made from a high-durability material to enable sustained transmission of the forces from the supercharged engine.
The forged pistons are only manufactured in very small numbers and, like the forged lightweight conrods, they're measured and weighed before being assigned to individual engines. This keeps any mass balancing tolerances to an absolute minimum. The pistons slide inside extremely durable, wear-resistant, low-friction cylinder barrels made from a special compound which is otherwise only found in race car engines. Twin oil injection is used for effective piston cooling.
The oil cooling technology employed for the power unit as a whole also draws on the brand's racetrack experience: a dry-sump lubrication system with a capacity of around 11 litres combines with a five-speed oil suction pump and a two-speed oil pressure pump to guarantee lubrication under all driving conditions. Dry-sump lubrication technology also enables a lower engine height for a lower centre of gravity and better handling.
Screw-supercharging
Efficient cylinder charging is the task of a belt-driven supercharger with two screw-shaped, Teflon-coated aluminium rotors. For efficiency's sake, the intelligent engine management system which independently determines when to deploy the screw compressor as the engine's rev speed and load change. Consequently, the supercharger is only called into action when needed -- although maximum power is available when throttle meets carpet.
The electronics also optimise the intercoolers' water cooling circuit for more efficient supercharging.
Performance
The SLR 722 Edition sprints from 0 to 62mph in a stunning 3.6 seconds compared to the standard SLR's 3.8 seconds, and 125mph (200 km/h) in 10.2 seconds (SLR 10.6 seconds). It hits 187.5mph (300 km/h) in 28.0 seconds (SLR 28.8 seconds) -- while the Vmax of 211mph is a smidge higher compared to the slower car's 209mph. Not that you're likely to notice...
Chassis setup
One of the main driving forces behind the car's improved performance is its retuned chassis. Working from the SLR's standard chassis, the F1 boys in Woking added more negative camber in compression and less dive and squat under braking and acceleration.
Wishbones are made from forged aluminium, while cast aluminium is used for the wheel carriers. The anti-roll bar is positioned above the front axle where it is controlled via rocker arms, F1-style. This cuts installation space which smoothes airflow under the car.
Road-testing showed that the car could take stiffer spring rates and shock absorbers, plus a lowering of the body by 10 mm at both front and rear. The benefits are increased directional stability and improved handling dynamics: body roll on bends has been reduced by over 20 per cent, allowing the new SLR 722 Edition to corner at even greater speeds.
New 19-inch forged aluminium wheels also help to improve the handling dynamics of the special-edition model, their unique, palladium grey design highlighting the car's motor-racing heritage. Their lower weight compared to conventional wheels reduces unsprung masses and sharpens responsiveness. The bigger wheels allow the fitting of larger ceramic Brembo brake discs -- they're 390mm in diameter.
Bodyshell
The entire bodyshell, including the crash structures at the front and rear, the occupant cell, the swing-wing doors and the bonnet, is made from carbon-fibre-reinforced plastic (CRP), whose specific energy absorption is some four to five time higher than steel or aluminium. This allowed Mercedes-Benz to fit two 620-millimetre-long side member elements made from carbon fibre in the front structure of the SLR 722 Edition. These can absorb all the impact energy in a head-on collision without exceeding the maximum levels of deceleration that the occupants are able to withstand. In the event of an impact, the fibres of these two elements tear from front to rear to crumple in a carefully predetermined manner and thereby produce a constant rate of deceleration.
The occupant cell is also made from CRP and, at the rear, two internal side members made from laminated carbon fibre and a sturdy cross member ensure that the occupant cell remains virtually intact. The occupant protection system also encompasses adaptive front airbags, which are deployed in two stages depending on the severity of the impact, head/thorax bags and knee bags, as well as seat belt tensioners and belt force limiters.
Aerodynamics
Around 100 hours of meticulous work in the wind tunnel also helped boost the performance of the SLR 722 Edition. Here the developers have increased downforce and reduced the cd (drag coefficient) via the new front air-splitter. Consisting of carbon with a clear-coat finish, the spoiler lip enhances aerodynamics and boosts downforce at the front axle by 128 per cent. Small wheel spoilers, also finished in carbon, reduce air swirl at the rear axle, making for a smoother airflow and optimising road feel. The spoilers combine with the airbrake at the rear to produce a further substantial gain in the rear downforce for more precise handling and turn-in at high speeds.
The rear-mounted airbrake is designed to optimise directional stability and braking power and rises at 75mph. If the driver hits the brakes hard at high speed, the airbrake tilts up into the airstream automatically. This dynamic modification increases rear-axle downforce within a fraction of a second, thus partially compensating for the front-end squat under braking.
The car's lighter too by 44 kg. A lighter oil tank and damper bodies made from aluminium, which also improve the vibration response of unsprung masses, contribute to this weight loss, along with optimised panelling and insulating materials.
Design
From the outside, the new wheels display the red callipers and brake discs, plus carbon bits and grille design link the car with F1 technology. It's available with a crystal antimony grey paint finish for what MB called "a vivid impression of depth and an extremely intensive-looking surface structure."
Inside, the bucket seats are upholstered in a combination of semi-aniline leather and Alcantara and offer lateral support. Colour contrast is provided by "300 SL red" stitching throughout the interior, the 722 insignia on the head restraints and red seat belts, all of which is echoed on the roof lining and door panels. Frequently used controls, such as the shift lever and handbrake lever, are trimmed in moisture-absorbing suede -- and there's lots of carbon bits scattered around the cabin.
A new instrument cluster with round dials showing information on a signal-red background along with a multi-function display gets and AMG Racetimer, along with a new steering wheel and aluminium shift paddles.
Yup, I thought so.
With Merc's power obsession, I'm very disappointed that this isn't a 722 bhp version.
And the wheels are pretty naff looking - much prefer the £10k optional vane design, which was after all supposed to improve brake cooling.
And on PH 6 months ago...............
MERCEDES TWEAKS THE SLR - Pistonheads 11/7/2006
(as if)
Now there are lots...this, CGT, Enzo, Veyron, Pagani Zonda F, Koenigsegg etc....I still cant buy any of em, and fiddly 'its a bit better' things just dont make me go 'ooh' anymore. shame really
Now there are lots...this, CGT, Enzo, Veyron, Pagani Zonda F, Koenigsegg etc....I still cant buy any of em, and fiddly 'its a bit better' things just dont make me go 'ooh' anymore. shame really
The Veyron admittedly has moved the whole game up another level compared to the SLR, Enzo and CGT, similar to what the F1 did in it's day to contemporaries like the XJ220, F40 and 959.
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