High performance in the business class – the new RS 6, together with its sister, the RS 6 Avant, is the most powerful series-production Audi ever. With an output of 426 kW (580 hp) and 650 Nm (479.42 lb-ft) of torque, it easily beats its competitors. The V10, which generates its output from 4,991 cc of displacement, is based on the engines fitted in the Audi S6 and S8, but it has been newly developed in virtually every detail. It is a conglomeration of glorious technologies that are taken directly from the world of motor sports – the ten-cylinder concept, FSI gasoline direct injection, the twin turbochargers and the dry-sump lubrication.
The two turbochargers – one for each cylinder bank – provide for extremely powerful, homogenous thrust, which is available across almost the entire engine speed range. The peak torque of 650 Nm (479.42 lb-ft) is available across a broad and high range from 1,500 to 6,250 rpm, while maximum output is generated in the range from 6,250 rpm to the maximum engine speed of 6,700 rpm.
The V10 biturbo engine gives a performance on a par with a high-performance sports car. It sprints from a standstill to 100 km/h (62.14 mph) in 4.5 seconds. After 14.5 seconds it breaks through the 200 km/h (124.27 mph) barrier. Not until a speed of 250 km/h (155.34 mph) has been reached is the acceleration ended by the electronic limiter – although Audi will raise this top speed on request to 280 km/h (173.98 mph). The power-to-weight ratio of the new RS 6 is also comparable to a high-performance sports car at just 3.4 kilograms (7.50 lb) per horsepower.
The ten-cylinder engine is a fascinating unit. Hanging closely and excitingly on the throttle, it spontaneously converts even the slightest pedal movement into powerful forward propulsion. The V10 is highly refined. When it is accelerating, its dual-branch exhaust system with its large oval tailpipes produces a striking, sporty sound that perfectly rounds out the profile of the RS 6 high-performance sedan.
The V10: The epitome of a sports car engine
A ten-cylinder engine is the ideal engine for maximum dynamism. Compared to a V8 unit with the same displacement, the V10 has shorter and lighter connecting rods, which give it refinement at high revs. On the other hand, it has fewer components than a comparable V12 engine, giving it a lower moving mass and lower internal friction. And it is far lighter and more compact in its construction – with all its ancillaries, the V10 is a mere 670 millimeters (26.38 in) long, 790 millimeters (31.10 in) wide and 655 millimeters (25.79 in) high. The basic engine block has a length of just 560 millimeters (22.05 in).
The V10 belongs to Audi's family of V engines, all of which have a 90 degree cylinder angle and 90 millimeters (3.54 in) cylinder spacing. The two banks are offset by 18.5 millimeters (0.73 in). The bore is 84.5 millimeters (3.33 in), the stroke 89.0 millimeters (3.50 in). The crankcase is especially complex in its construction. It is produced from over-eutectic aluminum alloy using the low-pressure die-casting method. This is a material that combines low weight with very high strength. The cylinder lines are honed by extracting the hard silicon crystals from the material. The complete engine weighs just 278 kilograms (612.89 lb).
An intermediate frame – a bedplate construction – gives the crankcase maximum torsional rigidity and further improves its vibrational characteristics. This incorporates bearing brackets made of gray cast iron. These reduce the expansion of the aluminum housing due to heat and keep the play in the main bearings of the crankshaft within tight limits. The configuration of the crankcase, with cross-flow cooling and without ventilation cross-sections between the crank chambers, boosts output and increases fuel efficiency.
The forged crankshaft with common pin – a crank pin spanning the full length –increases strength while reducing weight. The same thing applies to the high-strength connecting rods made of forged steel. The pistons, which bear newly developed ring packs, are cast from an aluminum alloy.
In order to satisfy the maximum demands with respect to driving dynamics, the oil supply for the V10 comes from a dry sump, a feature that is typical in motor sports. The external oil reservoir and the pump module, which operates with varying suction levels for the sake of efficiency, are extremely sophisticated in their configuration. This ensures that all components, including the two turbochargers, are reliably lubricated at all times – even during extreme lateral acceleration exceeding 1.2 g, which the new RS 6 is capable of.
Four adjustable camshafts: the valve drive
A hydraulic mechanism is used to allow all four camshafts to be continually adjusted by up to 42 crankshaft degrees to vary the valve overlap – improving charge level and combustion. The camshafts, the oil pump module and the ancillaries are driven via maintenance-free chains, which are located at the rear of the engine. The valves, which are actuated by roller cam followers with hydraulic valve-play compensation, have a diameter of 33.9 millimeters (1.33 in) on the inlet side and 28.0 millimeters (1.10 in) on the exhaust side. The exhaust valves, which are subjected to very high thermal loads, are filled with sodium for better cooling.
Like most of Audi's gasoline engines, the V10 in the new RS 6 also employs the FSI gasoline direct injection system. A common rail system – another standard for the brand – injects the fuel into the combustion chambers with a pressure of up to 120 bar.
Vacuum-controlled charge-movement flaps in the flange of the intake manifold, which is made of pressure-cast aluminum, set the drawn-in air into a "tumble" at up to 3,500 rpm. This rotational movement vertical to the cylinder axis improves combustion efficiency.
FSI is combined with turbochargers to make TFSI – both technologies harmonize perfectly. The swirl of the fuel draws heat from the walls of the combustion chambers, which resolves the old problem of turbocharger technology: excessive heat development. At 10.5:1, the compression ratio of the V10 in the new RS 6 is greater than in most naturally aspirated engines. This results in highly efficient combustion. The V10 biturbo consumes on average 13.9 liters of fuel per 100 km (16.92 US mpg) – a very respectable figure considering the potency of the vehicle. In motor sports, Audi's TFSI technology has enjoyed an astounding series of victories. It has powered the R8 racing car to five overall victories in the Le Mans 24 Hours and to 63 other successes in 80 starts.
In the new Audi RS 6, the V10 TFSI is controlled by an advanced Motronic engine management system with the designation MED 9.1.2. This works with ten single-core ignition coils and two control units operating according to the master-slave concept. Here, for the first time in this class, the load is monitored using a pressure sensor in the intake manifold. Two primary and two main catalytic converters assume the task of cleaning the exhaust gases. Because they are located close to the engine, they reach their operating temperature, and thus their full efficiency, very quickly after the engine is started.
The two large turbochargers are also high-performance components. They build up a charge pressure of up to 0.7 bar. At full load they are theoretically able to compress up to 2,200 cubic meters (77,692.26 cu ft) of air per hour. The chargers, and the complete air ducting, are optimized for a spontaneous, practically lag-free response. Air flows to the two large intercoolers, which reduce the temperature of the compressed air, through large inlet openings in the front apron.
Leave a comment