Performance and fuel consumption, power delivery and exhaust emissions, engine sound and characteristic Mercedes reliability - the AMG 5.5-litre V8 biturbo engine in the new SL 63 AMG meets the widest variety of requirements in all areas. This is made possible thanks to a combination of innovative high-tech systems such as direct petrol injection, twin turbochargers with air/water intercooling and the ECO start/stop function. The eight-cylinder engine develops maximum power of 395 kW (537 hp) and maximum torque of 800 Nm. For the first time the Performance package is also available for the SL 63 AMG, which increases the values to 415 kW (564 hp) and 900 Nm. As a result the new AMG Roadster offers more power than any of its competitors in this segment. The variant with the AMG Performance package also boasts increased charge pressure which has been pushed from 1.0 to 1.3 bar, and a high-quality real carbon-fibre engine cover, among other features. The key to this performance is the AMG 5.5-litre V8 biturbo engine, designated as the M 157, which premiered in 2010 in the S 63 AMG and CL 63 AMG.
It has also been the dynamic driving force behind the E 63 AMG and CLS 63 AMG. The M 157 is a paragon of efficiency and boasts a wealth of technological highlights. On account of higher thermodynamic efficiency, the combination of twin turbochargers, direct petrol injection and spray-guided combustion allows better fuel economy and results in lower exhaust emissions. An electric low-pressure pump sends the fuel from the tank to a high-pressure pump in the engine compartment at a pressure of 6 bar. The pressure of the fuel in the high-pressure rail is fully variable on demand between 100 and 200 bar, ensuring agile response in any driving situation. Further highlights of the innovative and unique eight-cylinder powerplant from Affalterbach include an all-aluminium crankcase, four valves per cylinder with camshaft adjustment, air/water intercooling, alternator management and the standard-fit ECO start/stop function. Whereas the previous AMG 6.3-litre V8 naturally aspirated engine had a displacement of 6208 cc, the new AMG 5.5-litre V8 biturbo engine needs just 5461 cc. Two exhaust gas turbochargers located next to the cylinder banks supply the eight cylinders with fresh air.
At their maximum speed of 185,000 rpm under full load, the two turbochargers force 1750 kg of air per hour into the combustion chambers. The maximum charge pressure is 1.0 bar, or 1.3 bar if the AMG Performance package is included. Thanks to their special, compact design - the turbine housings are welded to the exhaust manifold - there are significant space advantages, and the catalytic converters also heat up more rapidly. The AMG V8 dispenses with the usual blow-off valve. This neat solution has enabled the compressor housing to be made extremely compact. To ensure agile responsiveness with no time lag, all the air ducts in the intake tract are as short as possible. The AMG experts have enabled the wastegate valve, which reduces the pressure in the exhaust system during negative load changes, to be vacuum-controlled via an electropneumatic converter. This allows dethrottling under partial loads, which in turn lowers the fuel consumption. As was already the case in the AMG 6.0-litre V12 biturbo engine in the SL 65 AMG, the eight-cylinder direct-injection unit uses particularly efficient air/water intercooling.
The low-temperature cooler with its water circulation is accommodated within the V of the cylinder banks to save space. It effectively cools down the intake air compressed by the turbochargers before it enters the combustion chambers, and maintains a constantly lower intake temperature under full load. The large radiator at the car's front end ensures defined cooling of the water circulating in the low-temperature circuit. Extremely short charge-air ducting makes for optimum responsiveness. The stainless-steel pressure pipes for the fresh and charge air are produced by the hydroforming process, have a wall thickness of only 0.8 millimetres and are designed for very low pressure loss. The crankcase for the AMG 5.5-litre V8 biturbo engine is made of diecast aluminium. The low (dry) engine weight of 204 kilograms is the result of uncompromising lightweight construction methods and gives the vehicle balanced weight distribution. The bearing cover for the main crankshaft bearings, made of grey cast iron, is bolted to the crankcase for high rigidity. Cast-in Silitec cylinder liners ensure that the eight pistons operate with low friction.
Drilled ventilation holes in the crankcase lead to a higher output and fuel savings under partial load: above the bearing blocks there are longitudinally drilled holes which connect the adjacent crankcase cavities. Normally the upward and downward movement of the pistons causes air to be forced into and extracted from the sump, which leads to increased resistance and therefore a reduction in output. The ventilation holes prevent this by ensuring effective pressure compensation between the cavities. Perfect charging of the combustion chambers is ensured by large intake and exhaust valves, of which there are two per cylinder. The exhaust valves, which are subject to high thermal loads, are hollow in order to reduce weight and also sodium-cooled. Four overhead camshafts operate the 32 valves via low-maintenance, low-friction cam followers. The continuously variable camshaft adjustment within a range of 40 degrees on the intake and exhaust sides depends on the engine load and engine speed, leading to outstanding output and torque values. This also results in consistent idling at a low speed.
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