Development Goals and Design of the New 5.5-Litre V8 Biturbo Engine

Emotional peak performance and enormous torque, agile power delivery and a characteristic engine sound, comfort on long journeys and hallmark Mercedes reliability: expectations are high when Mercedes-AMG introduces a new high-performance engine – and its very first biturbo eight-cylinder is no exception. Two criteria are inexorably gaining in importance, namely efficiency and economy. Mercedes-AMG is confronting the challenges of the future, and demonstrating that dynamic performance can be perfectly combined with fuel economy.

The new AMG 5.5-litre biturbo engine combines performance with efficiency to a previously unknown extent. This is made possible by a unique combination of innovative high-tech systems such as direct petrol injection, twin turbochargers, air/water intercooling and the Controlled Efficiency start/stop function. The eight-cylinder biturbo engine will celebrate its market debut in the new S 63 AMG in September 2010.

Mercedes-AMG is systematically following the trend towards increasing efficiency with its new V8 biturbo engine: with a displacement of 5461 cubic centimetres it is precisely 747 cc below the 6208 cc of the naturally aspirated AMG 6.3-litre V8. Nonetheless it considerably betters it in terms of output and torque. The AMG 5.5‑litre V8 biturbo engine develops a peak output of 400 kW (544 hp) and maximum torque of 800 newton metres. In conjunction with the AMG Performance Package these figures increase to 420 kW (571 hp) and 900 newton metres. The torque curve in particular shows that no other engine in this output class is able to match the figures delivered by the new Mercedes-AMG biturbo unit.

Despite an increase in output by 14 kW (19 hp) resp. 34 kW (46 hp) and in torque by 170 and 270 newton metres compared to the naturally aspirated V8, which develops 386 kW (525 hp) and 630 newton metres, AMG engineers have been able to reduce fuel consumption and CO2 emissions considerably.

With a provisional NEDC fuel consumption of only 10.5 litres per 100 kilometres, the new S 63 AMG betters its predecessor by 3.9 litres. This equates to a fuel saving of more than 25 percent, which engine specialists consider to be nothing less than a quantum leap. CO2emissions have likewise been significantly reduced: at 246 grams per kilometre, the figure is 28.5 percent lower than for the previous model (344 g/km).

The achievement of these efficiency and environmental aims has no negative
effects whatsoever on dynamic performance. On the contrary, as the new AMG 5.5-litre V8 biturbo fully lives up to AMG’s brand commitment to “performance”: the S 63 AMG accelerates from zero to 100 km/h in 4.5 seconds, and has a top speed of 250 km/h (electronically limited). With the AMG Performance package, the high-performance saloon reaches the 100 km/h mark in 4.4 seconds and reaches a top speed of 300 km/h (electronically limited).

Key figures at a glance:*

* provisional figures; ** electronically limited

Combination of twin turbocharging and direct petrol injection

Mercedes-AMG is presenting an attractive high-tech package with its combination of biturbo charging and direct petrol injection with spray-guided combustion. The innovative injection technology brings decisive advantages with respect to fuel consumption and exhaust emissions, thanks to higher thermodynamic efficiency. Particularly fast and precise piezo-electric injectors spray the fuel into the combustion chambers, ensuring a homogeous fuel/air mixture and highly effective combustion.

An electric low-pressure pump delivers the fuel from the tank to a high-pressure pump in the boot with a pressure of six bar. The fuel pressure in the high-pressure rail is controlled between 100 and 200 bar on a fully variable and demand-related basis.

Two turbochargers and efficient air/water intercooling

Two 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 into the combustion chambers per hour. The maximum charge pressure is 1.0 bar, and 1.3 bar with the AMG Performance
package. Thanks to their specific, compact construction – the turbine housings are welded to the exhaust manifold – there are significant space advantages and the catalytic converters also heat up more rapidly.

The new AMG V8 is the first turbocharged engine to dispense with the usual blow-off valve. This neat solution 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 wastegate valve, which reduces the pressure in the exhaust system during negative load changes, is 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, the new eight-cylinder direct-injection unit uses particularly efficient air/water intercooling. The low-temperature cooler with its water circulation is space-savingly accommodated within the V of the cylinder banks. It effectively cools down the intake air compressed by the turbochargers before it enters the combustion chambers, and maintains a constantly low intake temperature under full load. A large radiator at the car’s front end ensures defined cooling of the water circulating in the low-temperature circuit. This guarantees a high output and torque yield in all ambient temperatures and operating conditions. Extremely short charge air ducting makes for outstanding 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 particularly low pressure loss.

Aluminium crankcase with Silitec cylinder liners

The crankcase of the new AMG 5.5-litre V8 biturbo engine is of diecast aluminium. The low (dry) engine weight of just 204 kilograms is the result of uncompromising lightweight construction methods, and leads to the car’s very balanced weight distribution. The bearing cover for the main crankshaft bearings is of grey cast iron, and is bolted to the crankcase for high rigidity. Cast-in Silitec cylinder liners ensure that the eight pistons operate with low friction. Drilled pulsation 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 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 internal friction losses and therefore a reduction in output. The pulsation holes prevent this by ensuring effective pressure compensation between the cavities.

The forged crankshaft of high-grade 38MnS6BY steel alloy rotates in five main bearings, has eight counterweights and has been optimised with respect to torsional rigidity, inertia, low rotating masses and a long operating life. A two-mass viscous damper mounted at the front reliably eliminates vibrations. Each connecting rod journal on the crankshaft carries two forged, cracked connecting rods. In the interests of low mechanical friction and high wear resistance, the lightweight pistons have a metallic contact surface. Pressure-controlled oil-spray nozzles in the crankcase ensure that the highly stressed piston crowns are efficiently cooled.

Four-valve technology with variable camshaft adjustment

Perfect charging of the combustion chambers is ensured by large intake and exhaust valves, of which there are 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 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. 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 electromagnetically via four pivoting actuators, and is controlled by the engine control unit. The camshafts are driven by three high-performance silent chains, which have considerable advantages in noise comfort compared to cylinder roller chains.

Efficient oil supply and water cooling

Efficient oil delivery under all load and operating conditions is ensured by an oil pump with an electrically controlled compression stage. The oil pressure can be varied between two and four bar, which has advantages in terms of friction and fuel consumption. An extraction stage integrated into the oil pump for the two turbochargers prevents oil from being entrained into the charge air and exhaust gases, thereby helping to reduce emissions even further. Both the sump and the extraction point have been optimised for maximum lateral acceleration and efficient lubrication. The oil capacity is 10.5 litres.

The combined water/oil cooling system is a particularly clever solution: initially the engine oil only flows through the oil/water heat exchanger. If the cooling performance of the very compact cooler is insufficient, the flow is directed through the external engine oil/air cooler by an oil thermostat. The advantage of this system is that the engine oil warms up more rapidly, as the engine coolant warms up faster and the oil is later cooled by the coolant. A selectable water thermostat ensures rapid warming of the coolant when starting the engine and driving off.

The engine coolant is cooled on the particularly effective crossflow principle. There is a transverse flow of coolant through both the crankcase and the cylinder heads. Additional cooling slots in the cylinder head ensure more efficient cooling of the combustion chambers, which has advantages during combustion: it enables earlier ignition timings to be chosen without incurring the risk of knocking.

Highly efficient engine electronics for every function

All the engine functions are executed and controlled by a particularly efficient Bosch MED 17.7.3. control unit. This state-of-the-art engine computer not only controls the direct petrol injection, charge pressure, camshaft adjustment and variable oil supply, but also communicates with all the other onboard control units. The microprocessor has more than 30,000 different parameters and functions stored in its memory, and is able to perform up to 260 million individual operations per second. To reduce the load on the engine control unit, the eight individual ignition coils have an integral electronic module known as an ignition amplifier at each cylinder. These ensure a strong ignition spark at all engine speeds and under all load conditions. Eight high-voltage powerstages are responsible for highly precise fuel distribution to the piezo-electric injectors.

Effective emissions technology with new catalytic converter boxes

Low exhaust emissions, compliance with country-specific standards and a characteristic AMG engine sound – the requirements for the exhaust system of the new AMG 5.5-litre V8 biturbo engine were manifold and complex. The S 63 AMG complies with all the current EU-5 emission standards, as well as meeting all the requirements of the US market (LEV-II standard, On-Board Diagnosis II and lambda sensor diagnosis).

The turbochaders are welded to the exhaust manifolds, while air gap-insulated manifolds with a wall thickness of only 1.0 millimetre ensure a rapid catalytic converter response. For efficiency and to save space, this concept 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 solution 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.

The lambda sensors are necessary for demand-related lambda control. In all operating conditions, the constituents of the intake mixture can be precisely controlled to avoid damaging the catalytic converters. This also benefits the fuel consumption under full load, as the mixture can be leaner than in engines without this control system.

Twin-pipe AMG sports exhaust system for a characteristic sound signature

The twin-pipe AMG sports exhaust system has a pipe cross-section of 70 milli-metres from the manifolds to the rear silencers. When designing the sound, the aim was to create a perfect synthesis of perceived dynamism and the comfort on long journeys that is the hallmark of a Mercedes. The goal of the developers was to achieve an emotional experience when accelerating and double-declutching, but unobtrusiveness at constant speeds. Unpleasant frequencies or droning noises were effectively eliminated during a series of painstaking tests. As a result, the striking pair of twin tailpipes of the AMG sports exhaust system emit a sonorous eight-cylinder sound that is typical of AMG.