The Mercedes SLR McLaren
by Marcus B. Fitzhugh
In the 1950s, Mercedes-Benz built a legend - the 300 SLR Coupe. Many people confuse this with the 300SL gull-wing (known internally as the W198). The gull-wing was also renowned. The 300SL gull-wing was introduced in 1954, had gull-wing doors, and was the fastest production car on the planet. It was also the first gasoline powered car with direct injection. Yes, fifty years ago Mercedes-Benz introduced what some people tout as "new technology" today. The 300 SLR was a different beast where the R stood for Rennen, or Race in English.
The history of the 300 SLR was short. It won the 1955 Mille Miglia (an Italian race that covered a thousand miles), Targa Florio, and a number of other races before eventually winning the 1955 World Sportscar Championship. In 1956 Mercedes-Benz withdrew from motorsport. Mercedes-Benz withdrew because during the 1955 running of the 24 Hours of Le Mans, an SLR was involved in a horrific accident that resulted in the death of the SLR driver and eighty-four spectators. Although the accident was neither the fault of Mercedes-Benz nor its driver, Mercedes-Benz pulled out of racing for several decades.
In 1993, Mercedes-Benz began supplying F1 engines. The return to Formula One racing resulted in a partnership between Mercedes-Benz and McLaren. That partnership eventually resulted in the Mercedes SLR McLaren.
Starting an SLR is a deliberate procedure. One that gives the driver a moment to consider the beast they are about to awaken. After turning the ignition on, lifting the cover on the shift lever, and then the pressing the button, the engine comes to life. At that point, it's a very good idea to plot a course before engaging the warp drive.
The warp drive comes courtesy of an all-aluminum, hand-built, 5.4 liter, supercharged, SOHC V8 engine. As with all M113 V8's, this has three valves per cylinder. The bore and stroke specs are standard for an AMG 55 - 97 mm (3.82 inches) on the bore and a 92 mm (3.62 inches) stroke. This engine differs from the standard AMG M113 55K in a number of ways. Two things that immediately stand out are its dry sump oiling system and the Lysholm-type twin-screw supercharger.
A dry-sump system was selected to ensure the engine always receives an adequate supply of oil. The cornering capability of the SLR is such that G forces could cause the oil to draw to the side of a standard oil pan, thereby allowing the oil pickup to suck air. With a dry-sump system, this is no longer possible. The dry-sump also reduces engine height. This allows the car to have a lower center of gravity.
The engine has a belt driven supercharger that rests between the two cylinder banks. This particular supercharger can rotate at 23000 revolutions per minute, and produce 0.9 bar (13 psi) of boost. The compressed intake air is cooled by two intercoolers. The engine produces 617 HP and 575 pound feet of torque. Manufacturers regularly supply peak numbers that don't properly describe when the power is available. The SLR produces over 440 pound feet of torque as low as 1500 RPM. This number rises to over 515 pound feet of torque by 2000 RPM. 575 pound feet of torque is available from 3250 RPM all the way through 5000 RPM. As the engine nears the top of the rev range, 617 HP is available at 6500 RPM. This engine produces a lot of power throughout the rev range.
The transmission is an AMG SPEEDSHIFT R equipped 5-speed automatic. A rotary dial controls the three modes available: Comfort, Sport or Manual. In manual mode, shifting is controlled by switches mounted on the steering wheel. Those too have three options: Sport, SuperSport and Race.
After starting the engine and deciding which transmission mode to use, flattening the accelerator will cause 60 MPH to arrive in less than four seconds. Equally impressive is the fact that the car will pass the quarter-mile mark in 11.5 seconds at over 125 MPH. Eventually, the car will stop accelerating. At that point, the SLR will be traveling at over two hundred and five miles per hour.
In an effort to prevent their customer base from killing themselves, Mercedes-Benz has included a number of safety features.
Engine placement is one of those features. The initial design was for a front engine car. That was changed to a front-mid mount design. The engine was moved one meter rearward (39.4 inches) of the front bumper. This placed it about 50 centimeters (19.7 inches) behind the front axle. Cars with a mid-engine design handle and brake better than those with either a front or rear engine design.
In a supercar, braking is more important than acceleration. The SLR features the Mercedes-Benz Sensotronic Brake Control system (SBCTM). Sensotronic is an electrohydraulic system that processes data from various sensors regarding the current state of the vehicle. Sensotronic can use this data to calculate and distribute optimum brake pressures for each wheel. SBC uses a high-pressure accumulator to hold the brake fluid, which when released, flows into the system at a pressure between 140 to 160 bar. SBC also optimizes the functionality of the Electronic Stability Program (ESP®). ESP keeps the SLR safely on track by applying targeted brake impulses to the individual wheels and reducing engine torque. The combination of SBC and EPS offers the advantage of greater braking power and precise use of that power.
At each corner, carbon fiber/ceramic brake discs are used. These discs offer superior braking performance, thermal resistance, and durability when compared to steel discs. Those discs are squeezed by eight-piston calipers up front, and four piston calipers out back. The braking system has sensors that detect water. When wet, the system automatically uses the calipers to dry the discs. On top of all that, the SLR is equipped with an automatic air brake.
Has the combination of high tech alloys, hard to decipher hardware, and the alphabet soup of acronyms got you confused? Here's the condensed version - the SLR has the most advanced braking system of any production car on the planet.
Braking is dependant on traction. Traction is dependant on suspension. The SLR's suspension is the absolute best design in the world. The SLR uses a double wishbone suspension for both the front and rear. The lower struts are arranged so that, as the springs compress and when cornering at speed, the wheels have a negative camber. This ensures the best possible contact with the road in every situation. At the same time, the axle technology prevents the front of the car from diving during heavy braking, and the rear from diving when accelerating.
The wishbones on the SLR are made from forged aluminum, while the wheel mounts are made of cast aluminum. An aluminum double wishbone design has a number of advantages over conventional steel designs. Practically speaking, the lightweight nature of aluminum allows the suspension to react significantly faster and to respond more sensitively.
The SLR has a relatively long wheelbase - 2700 millimeters. This gives the SLR's exceptional directional stability, something that is especially appreciated at speeds north of 150 MPH. Coupling this with the car's wide track width and low center of gravity allows for high cornering speeds.
The SLR's front/rear spring and damper combinations and itss front sway bar round out the suspension structure. The sway bar is positioned above the front axle and, as in Formula 1, is controlled by rocker arms. This means that it does not take up any installation space that could impair the smooth line of the underbody. This was a vital factor when designing the car's outstanding aerodynamic properties.
The SLR has speed-sensitive rack-and-pinion power steering that coincides with the car's lightweight design. In comparison with other steering systems, this design has a significantly lower weight. Due to itss low installation position in front of the engine and itss 12.6 gear ratio, the steering system offers excellent response and very high precision. Driver comfort is a big part of vehicle safety. With that in mind, the three-spoke steering wheel is 380 millimeters in diameter and has an electric motor that allows it to be positioned to suit the individual driver. The steering wheel can be adjusted by 60 millimeters for reach, and the height of the steering wheel can be varied by 2.7 degrees.
The SLR is a supercar. Supercars are typically driven at very high rates of speed. Despite the world's most technologically advanced brakes and a great suspension system, occasionally someone is going to hit something. Mercedes-Benz has addressed this inconvenience with a number features that should ease the pain of accidents.
In addition to the initial model, there were several other versions of the SLR.
The 722 Edition was introduced in 2006 and featured upgraded styling and performance. The "722" pays homage to the victory by Stirling Moss and his co-driver Denis Jenkinson in a Mercedes-Benz 300 SLR. That car had a starting number of 722, which was used to indicate a start time of 7:22 AM at the Mille Miglia in 1955.
The 722 Edition's engine produced 640 hp @6500rpm and 600 lb-ft of torque @ 4000 RPM. This car had a top speed of 209 MPH (337 km/h), which was marginally higher than the standard SLR. It was also slightly faster at lower speeds. Lighter weight wheels were used to reduce unsprung weight, and the suspension was modified. Shocks with stiffer damper settings, and a 10 mm (0.39 inch) lower ride height produced improved handling. Larger 390 mm (15 inch) diameter front brake discs, a revised front air dam, and rear diffuser were added.
Visually, the 722 can be car recognized by itss 19-inch black wheels, red "722" badges, and slightly different head and tail lamps.
Mercedes SLR McLaren Roadster
A roadster version was offered in September 2007 for something in the neighborhood of $700,000 (U.S.). It uses the same supercharged V8 AMG power plant and has the same acceleration/top speed figures. With that much power on tap, the additional weight of the roadster conversion wasn't really an issue.
The extra weight does impact handling, but not below "take me to jail now" speeds. The SLR Roadster's roof is not the folding metal design as used on the SL and the SLK. itss a soft top. At seven hundred large, I don't think very many SLR Roadster's will see rain duty. To lower the roof, latches are manually unfastened, a button is pressed, and in 10 seconds the roof electrically folds away. According to the Mercedes-Benz press kit, the occupants of the roadster can have a casual conversation at normal voice levels up to a speed of 120 mph with the top down.
Mercedes SLR McLaren Roadster 722 S
In 2009, a limited 150 unit version of 722 coupe was released. This model has the same low speed performance numbers of the 722 (albeit with a one MPH reduced top speed), with the open air convenience of the Roadster.
Mercedes SLR McLaren 722 GT
In 2007, the SLR 722 GT was released. The SLR 722 GT is a tuned version of the SLR 722. These were developed for a single manufacturer racing series. With approval from Mercedes-Benz, the cars were built by Ray Mallock Ltd. This model has wider bodywork to accommodate OZ racing wheels. The front grill vents are removed and larger, freer flowing air extractors are on the hood and side of the car. A racing wing and diffuser were added to the rear.
These cars are 880 pounds lighter and weigh in at 2,900. The engine internals are basically stock, but thanks to increased boost (1.75 bar) they produce 670 hp and 610 lb-ft of torque. The interior of the car is stripped of everything that isn't absolutely necessary. A carbon fiber seat, door panels, and a full roll cage replace the standard 722 inner sanctum.
Renntech announced they would be the exclusive distributors of the 21 SLR McLaren 722 GTs made available to North American consumers. For $1.2 million US dollars, itss all yours.
Mercedes SLR McLaren Stirling Moss
The SLR Stirling Moss is a limited edition, and there are only 75 cars. Introduced at the 2009 North American International Auto Show, this model has a speedster styling and does not include roof or windshield. The design was inspired by the 300 SLR racecar. This is the last series of the SLRs.
The engine has 640 hp, the top speed is increased to 220 MPH and lower speed acceleration is marginally faster. The Sterling Moss is about 440 lb lighter than the regular model.
The SLR Stirling Moss began production in June of 2009, a month after production ended for the SLR Roadster. The SLR Stirling Moss has an MSRP of about $1.1M US dollars and was only available to current SLR owners.
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