December 10, 2012

RS5 Cabriolet - Engine
Source: Audi Media

The 4.2 FSI in the Audi RS 5 Cabriolet combines high torque with spontaneous response and dynamic high-revving flexibility. The naturally aspirated V8 produces 430 Nm (317.15 lb-ft) of torque from 4,000 to 6,000 rpm. At 8,250 rpm, it develops 331 kW (450 hp) from 4,163 cc of displacement; the high-revving fun is not electronically limited until 8,500 rpm. The specific power output is 79.5 kW (108.1 hp) per liter engine displacement; each hp only needs to move 4.27 kg (9.41 lb) of vehicle weight.

The 4.2 FSI accelerates the Audi RS 5 Cabriolet from 0 to 100 km/h (62.14 mph) in 4.9 seconds. The car’s top speed is limited to 250 km/h (155.34 mph); at customer request, Audi can boost this to 280 km/h (173.98 mph). Despite its high performance, the powerful V8 delivers astonishingly high efficiency: in the NEDC cycle, the eight-cylinder unit has a combined fuel consumption value of 10.7 liters per 100 km (21.98 US mpg). The cylinder liners and the chain drive have been optimized for minimal friction, and the oil pump features need-based control.

Audi RS 5 Cabriolet: performance and fuel economy

0 – 100 km/h (62.14 mph), s


Vmax km/h

250 (155.34 mph) (optional 280) (173.98 mph)

Fuel consumption NEDC, l/km

10.7 (21.98 US mpg)

CO2 emissions, g/km (combined)

249 (400.73 g/mile)

Audi manually assembles the 4.2 FSI at its Hungarian engine plant in Györ. The engine features a classic cylinder angle of 90°; the two banks are offset by 18.5 mm (0.73 in). With a stroke/bore ratio of 92.8 mm (3.65 in) to 84.5 mm (3.33 in), the V8 has a long-stroke design. Its valve covers are painted red.

The high-performance V8 tips the scales at just 216 kg (476.20 lb). The forged-steel connecting rods, the pistons forged from a high-strength aluminum alloy and the forged crankshaft are lightweight yet extremely strong. The crankcase is produced in a low-pressure die-casting process that ensures very good material uniformity. Its aluminum-silicon alloy combines low weight with high strength. Its high silicon content makes the cylinder liners extremely wear-resistant.

In the crankcase, with its bedplate design, a frame supports the bearing blocks for the crankshaft, ensuring maximum strength and optimal vibration characteristics. The cast iron bearing blocks control thermal expansion of the crankcase, which maintains play at the main bearings of the crankshaft within tight limits.

Like all Audi gasoline engines, the fuel is distributed to the 4.2 FSI by means of common-rail direct injection. The fuel swirls intensely in the combustion chambers, which cools the chamber walls. This process minimizes the risk of autoignition of the mixture on hot spots. This results in an exceptionally high compression ratio of 12.5 : 1, which has a beneficial effect on both performance and efficiency.

The four camshafts, which can be hydraulically adjusted through 42 degrees of crankshaft angle, are actuated by chain drives running on the back side of the engine. Roller-type cam followers actuate 32 large-diameter valves – 33.9 mm (1.33 in) on the intake side, 28.0 mm (1.10 in) with the sodium-cooled exhaust valves. The intake manifold is made of plastic.

The 4.2 FSI naturally inducts intake air and exhausts gases freely thanks to sophisticated fine-tuning on the twin-pipe intake and exhaust system with the two throttle valves. Vacuum-actuated tumble flaps are integrated into the intake ports. Controlled by the engine management system, they cause the intake air to flow with a cylindrical swirling motion at part load, which improves combustion speed and, in turn, efficiency.

The exhaust system pipes are produced from stainless steel using hydroforming; flaps are installed in the two large tailpipes. If they open at high load and revs – or at the push of a button in the Audi drive select system –, making the sound of the V8 even fuller. As an option, Audi can deliver the car with a sport exhaust system with black tailpipe trim, also with flap switching function.

Audi RS 5 Cabriolet: the 4.2 FSI

Displacement, cc


Bore/stroke, mm

84.5/92.8 (3.33 in/3.65 in)

Compression ratio


Power output, kW (hp)

331 (450) at 8,250 rpm

Torque, Nm

430 (317.15 lb-ft) from 4,000 to 6,000 rpm

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.

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