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| March 05, 2019 | Volume 15 Issue 09 |
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Refined muscle: New Mercedes-AMG GT R Roadster
Looking like a well-defined comic-book superhero, the new Mercedes-AMG GT R Roadster deftly melds high performance and a refined, stylish design. It's classy and yet ripped, straight from the gym -- but a high-end gym at that. The 577-hp V8 Biturbo features intelligent lightweight construction and highly dynamic handling. It's quick too. Zero to 60 mph in 3.5 sec.
The AMG 4.0-liter V8 Biturbo in the convertible delivers a maximum torque of 516 lb-ft, which is available over a wide range from 2,100 to 5,500 rpm. The eight-cylinder power unit delivers muscular performance in all engine speed ranges, combined with high efficiency. The exhilarating power delivery continues right up to the top speed of 197 mph.
Different exhaust gas turbochargers with modified compressor processing and a smaller boost pressure control valve cell, as well as sharper engine management application, are used compared with those found in the other AMG GT models. The boost pressure has increased by 2 psi. In addition, the exhaust ports have been optimized and the compression ratio modified. The entire combustion process has been retuned.
For optimum power output even when outside temperatures are high, Mercedes-AMG uses indirect air-to-water intercooling. With optimum flow of air and water, the intercoolers have a separate, two-stage low-temperature water circuit. The first cooler stage involves two parallel coolers in the left and right wheel arch.
The downstream charge air coolers, through which water flows, ensure that the intake air compressed by the turbochargers is cooled effectively before it enters the combustion chambers. It therefore remains at a consistently low level even under full load. Extremely short charge-air ducting makes for optimum responsiveness.
The combination of twin turbochargers and direct fuel injection with spray-guided combustion increases thermodynamic efficiency and output. Particularly fast and precise piezo injectors spray the fuel at high pressure into the eight combustion chambers. Multiple injection occurs on-demand, ensuring a homogeneous fuel/air mixture. The delivery of fuel is electronically controlled and fully variable for a fuel pressure between 100 and 200 bar.
The aluminum crankcase is produced using sand casting technology and features a closed-deck design. This ensures extreme strength while keeping the weight as low as possible, and allows high injection pressures of up to 140 bar. The NANOSLIDE coating on the cylinder liners is far harder than conventional grey cast-iron liners and therefore less susceptible to wear. In addition, its reduced friction in combination with the aluminum-forged pistons helps to increase efficiency. Four overhead camshafts control a total 32 valves.
The seven-speed dual-clutch transmission configured in transaxle layout at the rear axle has been made even more suitable for the racetrack by the AMG developers. First gear in the AMG SPEEDSHIFT DCT 7G has a longer ratio, while seventh gear and the final drive have shorter ratios to allow a more agile acceleration experience overall and very spontaneous response to fast accelerator pedal movements.
Using the AMG DYNAMIC SELECT gearshift paddle in the center console or the AMG steering-wheel buttons, the driver can adjust the AMG GT R Roadster to suit his or her individual requirements. They can choose from "Slippery," "Comfort," "Sport," "Sport plus," "RACE," and "Individual." The "RACE" mode optimally adjusts the shift strategy of the dual clutch transmission to the needs of racetrack usage -- very short shift speeds and highly dynamic engine sound are included. By pressing the separate "M" button in the center console, the driver can activate the manual transmission mode in any drive mode.
The AMG GT R Roadster also comes with AMG DYNAMICS. This integrated driving dynamics regulation expands the functions of ESP (electronic stability program) to exact dosing of power distribution at the rear axles and the characteristics of steering. In this way, the car becomes even more agile at its highest stability. AMG DYNAMICS optimizes the transverse dynamics by higher lateral acceleration, better traction, and load change reactions.
AMG DYNAMICS calculates how the vehicle will react. To do this, the system uses the available sensors that detect the speed, the steering angle, or the yaw rate, for example. Based on the pilot-control principle, it is possible to anticipate the vehicle behavior based on the driver's actions and the data from the sensors. The control system reacts in this way even before the driver -- and with no noticeable intervention of the system.
As for looks, noticeable right away is the low-slung front section and the AMG-specific radiator grille that create a distinctive "shark nose" impression and make the car appear to sit lower on the road. At the same time, this shape lowers the vehicle's back-pressure point, enhancing the flow of cooling air and the car's aerodynamic performance.
The standard LED High Performance headlamps strengthen the look with their light signature. A tri-functional, arched light functions as the daytime running light, navigation light, and turn signal. The multi-chamber reflector system with three single reflectors each for low beam and high beam not only ensures optimal illumination of the roadway, but also gives the Roadster a sporty, dynamic look, adding even more optical depth.
The V-shaped arrow-like appearance of the front end also gives the car the look of forward motion even while standing still. The front bumper in jet wing design along with the front splitter emphasize the car's width. The large outer air inlets in the front bumper guarantee a large supply of cooling air to the engine. For this reason, they sport two aerodynamically shaped horizontal fins in place of meshes, and as a result route the airflow to the radiators with minimal loss.
Additional Air Curtains on the outside of the front bumper calm the airflow, improving the cd value of the open-top two-seater. Thanks to their narrow, vertical openings, the Air Curtains also guide the air specifically toward the wheel arches, optimizing the flow properties. To ensure ideal airflow through the wheel arches, the roadster additionally features unique wheel arch liners with special cooling-air slits.
An active aerodynamics profile is concealed almost invisibly under the front of the engine. Weighing around 4 lb, this light carbon-fiber element is speed-sensitive and automatically extends around 1.6 in. downwards depending on the drive program. This process involves considerable change in the airflow and results in what is known as the Venturi effect, which "sucks" the car onto the road and reduces front-axle lift by around 88 lb at 155 mph. The aerodynamic profile automatically retracts again depending on the drive program and speed.
Especially during fast cornering and under high lateral acceleration, the vehicle delivers agile response with clear steering feedback, while remaining easily controllable. In addition, the drag coefficient is improved. The downforce on the rear axle remains at an unchanged high level.
When the electrically operated profile is extended, the radiator air outlet opens at the front and precisely guides air flow toward the double rear diffuser, which also benefits from an optimal flow of air. This improves the handling stability of the rear axle while reducing the temperature of the hotspots at the rear. At the same time, these aerodynamic measures ensure optimized stopping power by routing more cold air specifically to the wheel disks.
The active air regulation system AIRPANEL is a notable technical highlight. Vertical louvers at the bottom of the front bumper open and close electronically in around 1 sec to ensure the required amount of cooling. Constantly achieving the ideal position calls for highly intelligent and responsive control. During normal driving with no increased cooling demand, the louvers close for reduced drag, and air is directed at the underbody. Only when certain components reach predefined temps and the air demand is particularly high do the louvers open to allow maximum cooling air flow to the heat exchangers.
The super-light carbon front fenders add a total 1.8 in. of width to the roadster at the front compared with the AMG GT, and make room for the wider track and large wheel/tire combinations. A further distinguishing feature is the special wing signet featuring a fin and a large air outlet through which waste heat flows from the engine bay. This fin is perforated and incorporates the AMG diamond logo with five slats.
The side view benefits from the standard AMG Performance forged wheels in matte black. The especially lightweight 10-spoke wheel is exclusive to AMG GT R models, and its highly elaborate design includes a drop-center rim, a milled groove, and two high-sheen rim rings of different width. There are size 10.0 J x 19 ET56 wheels at the front and 12.0 J x 20 ET52 at the rear.
The brake calipers, which are painted yellow, can be seen through the wheels. The side sill panels make the vehicle look even lower on the road, while inserts in high-gloss black set an aggressive tone. The same applies to the high-gloss black caps on the door mirror housings.
The rear design also features numerous, noticeable differentiations. The aluminum sidewalls make this roadster 2.2 in. wider at the rear than the AMG GT. This creates room for the larger 20-in. wheels and tires as well as the wider track. These measures enable improved traction while allowing higher cornering speeds.
The large rear wing with an integral third brake lamp is fixed to the trunk lid and increases downforce on the rear axle. The airfoil mounts are painted in vehicle color, while the blade is finished in high-gloss black. Depending on the application or racetrack conditions, the inclination of the airfoil blade can be precision-adjusted in order to increase downforce on the rear axle.
The three-layered fabric soft top is supported by a lightweight magnesium, steel, and aluminum structure, which helps to keep the vehicle's center of gravity low. The inserted acoustic mat reduces noise.
The interior design echoes the exterior. The dashboard places a firm emphasis on width, creating an impression of a powerful wing. The driver is integrated into the cockpit thanks to the high beltlines, the door trims with their concave design, the dynamically rising center console, and the low seat position. The cockpit has the feel of a custom-fit superhero suit and made-to-measure shoes. In the center console a badge with the inscription, "1 of 750" points to the roadster's limited number of units. The standard-specification AMG Performance seats come in Exclusive Nappa Leather with Diamond Stitching.
The AMG GT R Roadster boasts fully digital instrument displays with an instrument cluster measuring 12.3 in. in front of the driver and a 10.25-in. multimedia monitor on the center console. The instrument cluster offers a screen design with the three AMG-specific display styles "Classic," "Sporty," or "Supersport."
The innovative, colored display buttons in the V-shaped center console integrate the display and control of transmission logic, suspension, ESP, exhaust system, aerodynamics profile, and start/stop function. Using TFT technology, the display buttons use intuitively comprehensible symbols to show the function, and are easy to operate with simply a small finger tap. The display buttons are supplemented by two rocker switches for the drive programs and volume control of the audio system.
The AMG GT R Roadster has also been given the new AMG Performance steering wheel as standard. It is characterized by its sporty design, a flattened bottom section with a heavily contoured rim, and intuitive operation. The steering-wheel rim is completely covered in DINAMICA microfiber. The galvanized steering wheel gearshift paddles allow an even sportier driving style with manual gear shifting. The integrated Touch Control buttons can be used to control the functions of the digital dash and the multimedia display by horizontal and vertical swipes of the finger. TRACTION CONTROL can be actuated via the right-hand controller. The selected setting is shown on the color LCD display directly integrated in the controller.
A key factor in a sports car's performance is a low gross vehicle weight. Mercedes-AMG uses an intelligent material mix in order to achieve this aim in the structure of the AMG GT R Roadster. Various aluminum alloys are utilized for the chassis and body, and magnesium for the front deck. This extremely light element at the front reduces the inertia ahead of the front axle, thus improving the vehicle's agility. The load-bearing structure of the trunk lid is SMC (Sheet Molding Compound) bonded with carbon fibers. These high-tech compounds excel with their lightweight design, high strength, and outstanding surface quality.
The weight-optimized spaceframe is made of die-cast and extruded aluminum sections. The high bending and torsional strength of the entire design enables extreme linear and transverse forces from the drivetrain and suspension to be absorbed and transferred. Unwanted flexibility is reduced, with the vehicle responding precisely and directly. The result is that the driver experiences a sports car with maximum dynamics with outstanding precision. The body-in-white now also has an integral aluminum cross member as rollover protection for the occupants.
Light and strong carbon fiber is also the material of choice for, among other things, the front fenders and the torque tube between the engine and transmission. Weighing in at approximately 30 lb, the carbon-fiber torque tube is about 40 percent lighter than its already weight-optimized aluminum counterpart in the AMG GT. As a structural component of the transaxle drivetrain, it creates a connection between the engine and the transmission with extreme flexural and torsional stiffness. It permits a direct connection of the drivetrain that is favorable to driving dynamics and plays a role in the vehicle's balanced weight distribution.
Further weight advantages come from the standard forged wheels, the titanium rear silencer, and fewer soundproofing materials.
The tunnel brace in carbon further stiffens the body considerably for withstanding the high torsional loads that occur during powerful acceleration. To this end, it braces the two vehicle sides against each other even more effectively in the tunnel area for the torque tube. This significantly increases the torsional rigidity by some 7.5 percent. After the first few feet, the driver gets an extremely precise driving impression, which is maintained even in the event of extreme vehicle loads when driving at the dynamic limits. The highly composed body allows for even better control of the AMG GT R Roadster under difficult racetrack conditions such as fast, bumpy corners and means that less steering effort is required.
Over and above this, two diagonal braces in the engine bay stiffen the front end. In the AMG GT R, they are also made of carbon fiber and represent weight savings of about 50 percent over steel components.
The specially developed AMG coil-over suspension can be precisely adjusted at the workshop. This technology, familiar from motorsport, is combined with the AMG RIDE CONTROL continuously variable, adaptive damping system. The system is controlled electronically and adjusts the damping at each wheel automatically to suit the current driving situation, the current speed, and the road or track surface. The driver can also adjust the adaptive damping characteristics at the touch of a button in the AMG DRIVE UNIT or by using the AMG DYNAMIC SELECT drive modes. Three modes are available: "Comfort," "Sport," and "Sport Plus."
So many more features. Limited to 750 units worldwide. No price released yet, but Motor Trend estimates it will run around $170,000.
Source: Mercedes-Benz
Published March 2019
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