The strong heart of the new RS 4 Avant has eight cylinders. The 4.2 FSI, which displaces 4,163 cc, combines excellent pulling power with instant response and an exhilarating willingness to rev, all backed by a widely differentiated, musical sound spectrum. The V8 produces 430 Nm (317.15 lb-ft) of torque from 4,000 to 6,000 rpm and puts out 331 kW (450 hp) at 8,250 rpm. The maximum torque is 8,500 rpm. The naturally aspirated FSI has a specific power output of 79.5 kW (108.1 hp) per liter of displacement; each hp only needs to move 4.0 kilograms (8.82 lb) of weight.
The 4.2 FSI accelerates the new top model in the A4 family from zero to 100 km/h (62.14 mph) in 4.7 seconds on its way to a governed top speed of 250 km/h (155.34 mph). This can be increased to 280 km/h (173.98 mph) upon request. The eight-cylinder engine averages 10.7 liters of fuel per 100 kilometers (21.98 US mpg) – 26 percent less than the previous model.
The technologies from the Audi modular efficiency platform are behind this impressive figure. The cylinder barrels and the chain drive are characterized by minimal friction, and the oil pump is demand-controlled.
The normally aspirated V8 is also a visual experience. Its cylinder head covers are painted red, and an optional carbon inlay adorns the intake plenum. The hand-built 4.2 FSI has a classic cylinder angle of 90 degrees. The two opposing banks are offset by 18.5 millimeters.
The V8 weighs just 216 kilograms (476.2 lb). The forged crankshaft, the forged steel connecting rods and the pistons forged from a high-strength aluminum alloy are all lightweight, yet strong. The crankcase is manufactured using the low-pressure die-casting method, which ensures particular homogeneity. The aluminum-silicon alloy combines low weight with high strength. Its high silicon content makes the cylinder barrels extremely durable.
The crankcase is configured as a bedplate construction. The lower bearing bridges for the crankshaft are integrated into a common frame for maximum rigidity and optimal vibration behavior. The cast iron bearing bridges reduce the thermal expansion of the crankcase and thus keep the play at the main bearings of the crankshaft within tight limits.
As in all Audi gasoline engines, fuel is distributed to the 4.2 FSI via common rail direct injection using FSI technology. The fuel is swirled intensively in the combustion chambers, which cools the walls. This process minimizes the risk of knock – the detonation of the mixture on hot spots. It allows a very high compression ratio of 11.0:1, which increases both output and efficiency.
Breathing freely: gas exchange
The long-stroke engine (bore x lift 84.5 x 92.8 mm [3.33 x 3.65 in]) can breathe freely in and out thanks to intensive refinements to the dual-flow intake and exhaust system with the two throttle valves. Vacuum-actuated tumble flaps controlled by the engine management system are integrated into the intake ports. Under partial load, they cause the air to move with a roller-like rotation, which increases the burning rate and thus the efficiency of the combustion process.
The four camshafts, which can be adjusted hydraulically through 42 degrees of crankshaft angle, are driven by chains running on the back side of the engine. The 32 valves, which are actuated via roller cam followers, have large diameters – 33.9 millimeters (1.33 in) on the intake side and 28.0 millimeters (1.10 in) in the case of the sodium-coiled exhaust values.
The Audi developers also adhered to the principles of ultra-lightweight construction for the peripherals of the 4.2 FSI. The intake manifold is made of polymers; a pressure sensor is used to measure the loads very precisely. The V8 gets by with only a single, newly developed controller.
The pipes of the manifold and of the exhaust system, which have been optimized for low backpressure, are hydroformed from stainless steel. A flap is integrated into each of the two large tailpipes of the dual exhaust system. At higher loads and engine speeds – or at the push of a button in the Audi drive select system – they open to provide a richer sound. Audi offers an optional sport exhaust system with black tailpipe tips that also includes this switching function.
The equipment and data specified in this document refer to the model range offered in Germany. Subject to change without notice; errors and omissions excepted.