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 ESP®, 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
Displacement5,461 cc
Bore x stroke3.86 in x 3.56 in
Compression ratio12.6 : 1
Output415 hp at 6,800 rpm
Max. torque398 lb-ft at 4,500 rpm
Engine weight (dry)412 lbs
Acceleration0 - 60 mph 4.5 s
Top speed155 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.

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