Mercedes latest roadster, the SLK55 AMG is powered by a naturally aspirated V8 producing 415 HP. Â We were hoping to see one of the latest Twin Turbo AMG motors or at least the 6.3 motor in the little roadster to really make things interesting and fun.
The 2012 Mercedes-Benz SLK55 AMG is the most powerful SLK of all time. Its new AMG 5.5-liter V8 engine featuring cylinder shutoff combines the ultimate in performance with the lowest possible fuel consumption. With a peak output of 415 hp and maximum torque of 398 lb-ft, the 2012 SLK55 AMG is poised to outperform all of its direct competitors. High-performance driving is ensured thanks to the AMG sports suspension with Direct-Steer system, Torque Vectoring Brakes and 3-stage ESPÂ®, as well as the AMG high-performance braking system. The 2012 SLK55 AMG will arrive in U.S. showrooms in early 2012.
Forming part of the third-generation of the SLK launched in June, the new AMG model catches the eye at first glance: distinctive AMG light-alloy wheels, exclusive AMG body styling with AMG spoiler lip and two chrome-plated twin tailpipes at the rear complement the classic roadster proportions, while adding a distinct athletic touch. The expressive design of the 2012 SLK55 AMG is both eye-catching and unmistakable.
The SLK55 AMG is the perfect embodiment of the new AMG brand claim of "Driving Performance": in the compact high-performance Roadster segment there is nothing to compare to its combination of tangible driving dynamics, superior sportiness, unique high-technology and low fuel consumption. The SLK55 AMG accelerates from zero to 60 mph in 4.5 seconds, and reaches a top speed of 155 mph (electronically limited).
Key figures at a glance
2012 SLK55 AMG
Displacement 5,461 cc
Bore x stroke 3.86 in x 3.56 in
Compression ratio 12.6 : 1
Output 415 hp at 6,800 rpm
Max. torque 398 lb-ft at 4,500 rpm
Engine weight (dry) 412 lbs
Acceleration 0 - 60 mph 4.5 s
Top speed 155 mph**
* provisional figures; ** electronically limited
Helping to set new fuel efficiency standards for V8's, the 5.5 liter engine combines low consumption figures with superior power delivery and the typical exhaust growl which only a large-displacement eight-cylinder engine can produce.
In line with its "AMG Performance 2015" strategy, the new V8 engine continues to reduce both the fuel consumption and emissions of new models over the next few years - while reaching new heights with the central brand claim of "Driving Performance". At the same time, AMG is also demonstrating its social responsibility with the M152 engine.
New naturally aspirated eight-cylinder closely related to the V8 biturbo
The new M152 is based on the AMG M157 5.5-liter V8 biturbo engine presented in 2010, which powers the E63 AMG, CLS63 AMG, S63 AMG and CL63 AMG. Numerous design features are identical, such as the displacement, bore/stroke, distance between cylinders, ECO stop/start system and direct gasoline injection technology. Distinguishing features versus the M157 include the new intake air ducting, new cylinder heads, the modified valve drive, an adapted oil supply system and an optimized crankcase.
Exclusive combination of advanced technologies
The high-tech M152 motor dazzles with a combination of advanced technologies which is unequalled anywhere in the world. No other gasoline engine features direct injection at a pressure of 2,900 psi, spray-guided combustion and piezo injectors, all in conjunction with map-controlled cylinder shut-off, an all-aluminum crankcase with "spectacle" honing, fourvalve technology with continuous camshaft adjustment, a high compression ratio of 12.6 : 1, a stop/start system and generator management - while revving to a maximum speed of over 7,000 rpm. All of these features lead to high thermodynamic efficiency which is essential for high fuel efficiency and low exhaust emissions. Using a large-displacement, naturally-aspirated eight-cylinder engine with cylinder shut-off resolves the trade-off between high output/torque delivery and low fuel consumption figures.
AMG Cylinder Management
The AMG Cylinder Management cylinder shut-off system - developed completely by Mercedes-AMG - significantly improves efficiency: cylinders two, three, five and eight are cut off under partial load, which lowers fuel consumption considerably. In similar form, this technology is also used in the 750-hp V8 engines used in Formula 1. As efficiency also plays a major role at the pinnacle of motor racing, two or four of the eight cylinders are cut off e.g. when cornering at slow speed, during Safety Car laps or for pit stops.
The cylinder shut-off function is available over a wide engine speed range from 800 to 3,600 rpm if the driver has selected transmission mode "C" - Controlled Efficiency. The AMG main menu in the instrument cluster informs the driver whether cylinder shut-off is active, and whether the engine is currently running in four or eight-cylinder mode. No less than 170 lb-ft of torque is still available in four-cylinder mode - enough power to ensure plenty of acceleration in most driving situations. As soon as the driver has a need for more power and leaves the partial load range, cylinders two, three, five and eight are activated. The switch from four to eight-cylinder operation is immediate and imperceptible, leading to no loss of occupant comfort. At an engine speed of 3,600 rpm the activation process takes no more than 30 milliseconds.
Valves closed, fuel delivery and ignition deactivated
Cylinder shut-off is made possible by the intelligent engine management system, with 16 hydraulically compensating actuators and a sophisticated oil supply system in the cylinder head. The compensating actuators are integrated into the cylinder head, and keep the intake and exhaust valves of cylinders two, three, five and eight closed when cylinder shut-off is active. At the same time their fuel supply and ignition are deactivated. This not only enables the loadchange losses of the four deactivated cylinders to be reduced, but also increases the efficiency of the four remaining cylinders. This is because the operating point is transferred to the higher load range. The actuators are compact and lightweight, allowing taut valve train operation and engine speeds up to 7,200 rpm.
All-aluminum crankcase with Silitec cylinder liners
The crankcase of the new AMG 5.5-liter V8 engine features a diecast allaluminum construction. The low (dry) engine weight of just 412 lbs is the result of uncompromising lightweight construction methods. The bearing covers for the main crankshaft bearings are grey cast iron, and are bolted to the crankcase, as well as on the sides, for high rigidity.
The piston rings are carbon-coated to minimize internal friction and reduce wear. Cast-in Silitec cylinder liners ensure low friction for the eight pistons. Unique "Spectacle" honing is another measure to reduce friction and therefore fuel consumption: in this sophisticated and complex process, the cylinder liners receive their mechanical surface treatment when already bolted in place. As honing would no longer be possible with the cylinder head installed, a jig resembling spectacles is bolted to the crankcase. The cylinder liners distort as if the cylinder head were in place, and are only then given their mechanical surface treatment. As a result, any static distortion of the cylinder liners caused by tightening the cylinder head bolts can be completely eliminated.
Other measures to optimize efficiency:
weight-optimized cast aluminum pistons with special piston skirt coating
special ventilation holes in the crankcase
oil pump with electrically controlled pressure stage
separate oil pump for cylinder shut-off as a controllable, low-friction vane cell pump
engine cooling using especially efficient cross-flow principle
electronically controlled fuel pressure, fully variable and demand-related between 1,450 and 2,900 psi
The forged crankshaft of high-grade 38MnS6BY steel alloy rotates in five main bearings, has eight counterweights and has been optimized with respect to torsional rigidity, inertia, low rotating masses and a long operating life. A twomass viscous damper mounted at the front reliably eliminates vibrations. Each connecting rod journal on the crankshaft carries two forged, cracked connecting rods.
Four-valve technology with variable camshaft adjustment
Perfect charging of the combustion chambers is provided by large intake and exhaust valves, four per cylinder. The exhaust valves, which are subject to high thermal loads, are hollow and sodium-cooled. Four overhead camshafts operate the 32 valves via low-maintenance, low-friction cam followers. The infinitely variable camshaft adjustment within a range of 40 degrees on the intake and exhaust sides adapts to engine load and engine speed, leading to high output and torque values. This also provides consistent idling at a low speed. Depending on the engine speed, valve overlap can be varied for the best possible fuel/air supply to the combustion chambers and efficient removal of the exhaust gases. The variable camshaft adjustment is carried out hydraulically via four pivoting actuators. These are electromagnetically activated and controlled by the engine control unit. The camshafts are driven by three high-performance silent chains, which have considerable advantages in terms of noise comfort compared with cylinder roller chains.
Controlled Efficiency stop/start function as standard
The Controlled Efficiency stop/start function further contributes to the low fuel consumption. This system is standard equipment on the SLK55 AMG and active in the fuel economy transmission mode "C". Once the driver brakes to a stop e.g. at a red traffic light, the V8 engine is automatically switched off. Once the brake pedal is released or the accelerator is depressed, the engine is immediately restarted and the car is able to move off quickly. Intelligent technology provides a comfortable and immediate starting procedure: a crankshaft sensor recognizes the direction of rotation and registers the resting position of all eight pistons. For an automatic engine start, the cylinder with the most favorable piston position receives an injection of fuel into its combustion chamber. The precise piezo-electric injectors greatly assist this process, as they make especially fast starts possible. The M152 always starts in eight-cylinder operation.
A framed "ECO" symbol in the AMG main menu shows the driver that the Controlled Efficiency stop/start function is active. When cylinder shut-off is active, the driver is informed by the symbol "ECO4", while "ECO8" stands for eight-cylinder operation. In the two more performance-oriented driving modes "S" (Sport) and "M" (Manual), the stop/start function is always deactivated. If required, the driver can also switch it off while in "C" mode as well. In this case neither a "stop/start" nor an "ECO" symbol appears.
Alternator management helps to save fuel
An alternator management system makes a further contribution to fuel economy: whenever the V8 engine is in overrun or when braking, kinetic energy is used to charge the battery rather than wasted as heat. In all other operating modes a combination of onboard network and alternator management enables the electrical system to be kept at a low voltage.
New AMG sports exhaust system with integrated exhaust flaps
AMG is premiering a new sports exhaust system featuring an exhaust flap on each side. This technology resolves the trade off between an emotional exhaust note during spirited driving and a more discreet engine sound in the partial load range. The main focus of the sound design was to achieve a perfect synthesis of perceptible performance and the long-distance comfort that is a hallmark of Mercedes.
Each of the two rear silencers has a flap which is variably activated on a logiccontrolled basis depending on the driver's power requirement and the engine speed. At low loads and engine speeds below 2,000 rpm the flaps remain closed. This causes the exhaust gases to cover a longer distance and flow through an additional damping element, so that the engine sound is pleasantly subdued and disruptive frequencies are effectively suppressed - resulting in a mellow tone especially in four-cylinder operation when cylinder shut-off is active.
When the driver accelerates, the flaps open at an angle of 15, then 30 and up to 50 degrees so that some of the exhaust gases cover a short distance while the remaining follow the longer, acoustically dampened path producing a sonorous engine note. Under full load at higher engine speeds in eight-cylinder mode, both flaps are fully opened so that the occupants are able to enjoy the distinct muscular sound typical of an AMG V8. This emphasizes the performance potential of the 415 hp naturally aspirated AMG eight-cylinder engine.
The two-pipe AMG sports exhaust system with two chromed twin tailpipes has a pipe diameter of 2.56 inches from the manifolds to the pre-silencer. The diameter is reduced to 2.36 inches from the pre-silencer to the rear silencers.
Effective emissions technology with new catalytic converter boxes
Low exhaust emissions, compliance with country-specific standards and a characteristic engine sound - the requirements for the exhaust system of the new, naturally aspirated AMG 5.5-liter V8 engine were multiple and complex. The 2012 SLK55 AMG complies with the current Euro-5 emission standard, as well as meeting all the requirements of the US market (LEV-III standard, On- Board Diagnosis II).
Air gap-insulated manifolds ensure a rapid catalytic converter response. For efficiency and to save space, this design has a tandem catalytic converter housing on each side of the vehicle: adjacent to the firewall, two thin-walled ceramic substrates are grouped into each housing. This setup makes the previous, additional underbody catalytic converters unnecessary. The two ceramic substrates differ to ensure rapid and efficient emissions control: the front one is coated with palladium, while the rear one has a bimetal coating of palladium and rhodium. One lambda sensor per row of cylinders is located in front of each catalytic converter housing, and there is a lambda diagnostic sensor between each of the two thin-walled substrates.
Highly variable: the AMG SPEEDSHIFT PLUS 7G-TRONIC
Power is transferred to the rear wheels by means of the AMG SPEEDSHIFT PLUS 7G-TRONIC automatic transmission which features three transmission modes: "Controlled Efficiency" (C), Sport (S) and Manual (M). The automatic rev-matching function when downshifting as well as the brief, precisely defined interruption of ignition and injection when upshifting under full load shorten shift times and increase emotional appeal. A double turbine torsional damper with centrifugal pendulum adapts to engine speed and helps minimize vibrations in four-cylinder operation as well as enhances comfort.
Perfect combination: highly expressive driving style and comfortable cruising
The AMG sports suspension with Torque Vectoring Brakes and AMG Direct- Steer system provides both impressive lateral dynamics as well as agile handling. Looking for a highly aggressive driving style or comfortable cruising? The new SLK55 AMG is able to offer both. Independent suspension struts with stiffer spring/damper tuning, torque strut bearings on the front axle featuring higher rigidity, stiffer stabilizers at all four corners as well as a more negative camber on the rear axle result in high cornering speeds and low body roll in fast S-shaped bends.
In critical cornering conditions, the Torque Vectoring Brakes produce a defined rotational movement of the vehicle about the vertical axis in fractions of seconds, through selective brake actuation at the rear wheel on the inside of the bend. This results in the SLK55 AMG steering into the turn precisely and under full control, without any compromises where performance is concerned. Complementing this feature is the AMG Direct-Steer system which enhances handling and agility compared with the standard steering, while also reducing the amount of physical effort required when parking. A new power steering pump helps to reduce fuel consumption by using energy only when the driver is actually steering. In addition, the AMG Direct-Steer system has a parameter function adapted to match the AMG sports suspension. This results in optimum response from the central position, outstanding road feel and sharp handling in all driving situations.
The AMG-exclusive 3-stage ESPÂ® gives individual control choices at the touch of a button: the ESPÂ® button in the center console allows the driver to choose between "ESP ON", "SPORT Handling Mode" and "ESP OFF". The AMG highperformance brake system has internally ventilated and perforated brake discs on all wheels, measuring 14.2 in. x 1.4 in. at the front and 13 in. x .9 in. at the rear. The system is characterized by outstanding responsiveness, short stopping distances and excellent fatigue resistance.
Optional AMG Handling Package for even greater driving dynamics
The optionally available AMG Handling Package enhances the vehicle's sportiness even further. It comprises an AMG Performance suspension with stiffer tuning, an AMG rear axle differential lock, two-piece brake discs at the front and a three-spoke AMG Performance steering wheel finished in premium leather with AlcantaraÂ® inserts in the grip areas.
Unmistakable: uniquely styled design and appointments
Classic roadster proportions with typical AMG design characteristics as well as a hint of the SLS AMG -are striking visual highlights of the 2012 SLK55 AMG. The AMG designers have complemented the exciting basic forms of the long hood, the greenhouse positioned well to the rear and crisp rear section with typical AMG styling at the front, sides and rear. The new AMG front apron has large air inlets and AMG-specific LED daytime running lights. Inspired by the SLS AMG super sports car, the wide radiator grill features a large, centrally-positioned Mercedes star. In the case of the SLK55 AMG, the slats in the front apron and the lower cross strut are painted in a high-gloss black finish. Darkened clear-lens headlamps and darkened bicolor tail lamps also come as standard exclusively on the top-of-the-range V8 model. Bi-Xenon headlights with Active Curve Illumination are also available as an optional extra.
The vent grilles with chrome-plated fins in the front fenders are not only reminiscent of the SLS AMG, but also evoke memories of the famous Mercedes- Benz 300 SL Roadster from the 1950s. The "V8 AMG" lettering beneath the grilles highlight the top-of-the-range eight-cylinder model from the rest of the SLK model series. AMG-specific, distinctively styled side sill panels continue the design of the front apron through to the new rear apron. With its own unique shape, black diffuser insert with three fins as well as the two chromeplated twin tailpipes of the AMG sports exhaust system, it gives a distinctive finishing touch to the vehicle. The spoiler lip on the trunk lid, painted in the vehicle body color, reduces lift at the rear axle and thereby increases driving stability at high speeds.
Inspired by the SLS AMG: high-quality, stylish interior
Functional, stylish, high-quality: the interior design of the SLK55 AMG is also reminiscent of its bigger brother, the SLS AMG Roadster. Associations with the super sports car are evoked courtesy of the four air vents in the style of jet engines, as well as the center console finished in brushed aluminum. Placed in the center of the dashboard is an AMG-specific analog clock featuring an IWC design. The AMG Performance steering wheel, with its flattened top and bottom sections, also boasts metal trim, aluminum shift paddles and grip areas finished in perforated leather. The clearly-arranged AMG instrument cluster is positioned perfectly in the driver's field of vision and features four circular instruments, distinctive dials and the AMG main menu. The button for the transmission modes C, S and M is also located in the center console.
The AMG sports seats feature optimized lateral support and premium leather upholstery with AMG badges in the backrests and standard AIRSCARF necklevel heating system.
Magical: the panorama roof with MAGIC SKY CONTROL
The standard retractable hardtop opens and closes in less than 20 seconds, transforming the open-top Roadster into a closed-top Coupe with rigid roof at the touch of a button. Alternatively, a panorama roof panel in tinted polycarbonate can also be chosen. The third variant is a world premiere - the panorama roof with MAGIC SKY CONTROL. This glass roof switches to light or dark as required at the press of a button. When activated it is virtually transparent, offering an open-air experience even in cold weather. In its dark state the roof provides welcome shade and prevents the interior from heating up from the sun's intense rays. In other words: a comfortable atmosphere at the touch of a button.
The frames of the three roof variants are made of magnesium. This makes each roof around 13 lbs lighter than in the previous model, giving the car a lower center of gravity - which benefits its agility. A comfortable alternative to the standard wind-stop is the new AIRGUIDE pivoting wind-stop. It consists of pivoting transparent plastic wings which are attached to the back of the rollover bars. The advantage: no installation or removal effort required.
Exceptional position: modern assistance systems on board
The 2012 SLK55 AMG sets new standards when it comes to safety: a whole host of the latest assistance systems support the driver and help secure the new AMG Roadster's exceptional position in its segment. Standard equipment includes new, fiber-reinforced roll-over bar, two-stage driver and front passenger airbags, headbags, thorax airbags, knee airbags, seat belt tensioner with belt force limiters, NECK-PRO crash-active head restraints, three-stage ESPÂ® and also ATTENTION ASSIST drowsiness detection.