The sportiest premium sedan in the full-size class – the new Audi A8
Engines
Powerful, efficient and highly cultivated – Audi is launching the new A8 in the German market with a choice of four engines. Both TFSI gasoline units and the two TDI diesels feature forced induction and direct injection. All engines intended for use in Europe satisfy the requirements of the Euro 6 emissions standard. The start-stop system is standard. Fuel consumption has been reduced by as much as 10 percent, yet power output has increased for most engines and now ranges from 190 kW (258 hp) and 320 kW (435 hp). Three additional models – the A8 L W12, the Audi S8 and the Audi A8 hybrid – round out the lineup.
The 3.0 TFSI: Spontaneous, sonorous, sporty
The intensively revised 3.0 TFSI steps up the power with 228 kW (310) hp and 440 Nm (324.53 lb-ft) of torque, the latter available between 2,900 and 4,750 rpm. The six-cylinder unit compresses the intake are using a supercharger located in the 90-degree V formed by the cylinder banks. Two intercoolers lower the temperature of the air again so that more oxygen enters the cylinders.
Compared with the previous engine, the new 3.0 TFSI produces 15 kW (20 hp) more power and consumes less fuel. Solutions such as a supercharger that can be shut down at low loads, adjustable intake and exhaust camshafts, a lower weight crankshaft, a higher 10.8:1 compression ratio and a package of measures involving the chain drive and the water pump, among other components, to reduce friction are responsible for this reduction in fuel consumption. The balance shaft, cylinder sleeves, oil pan and crankcase ventilation system have also been modified.
A major innovation in the 3.0 TFSI is the addition of indirect injection as a complement to direct fuel injection. It injects the fuel at the end of the flap flange in the vicinity of the tumble flaps, where it is swirled intensively with the air. The improved mixture formation this results in boosts fuel economy and reduces particulate emissions. Direct injection, which develops pressures up to 200 bar, is used when starting and at higher loads.
Powerful thrust, spontaneous response and a sonorous sound – the three-liter V6 with a displacement of 2,995 cc is a sporty engine. It accelerates the A8 from 0 to 100 km/h (62.14 mph) in 5.7 seconds (A8 L: 5.9 seconds). As with nearly all A8 models, top speed is a governed 250 km/h (155.34 mph). Average fuel consumption is 7.8 liters per 100 kilometers (30.16 US mpg), corresponding to 183 grams CO2 per kilometer (294.51 g/mile). These same figures for the A8 L are 7.9 liters (29.77 US mpg) and 184 grams (296.12 g/mile).
The 4.0 TFSI: COD reduces consumption
The 4.0 TFSI produces 320 kW (435 hp), 11 kW (15 hp) more than before. It delivers a 600 Nm (442.54 lb-ft) of torque to the crankshaft between 1,500 and 5,000 rpm. The 3,993 cc biturbo V8 accelerates the new A8 from 0 to 100 km/h (62.14 mph) in 4.5 seconds. The A8 L completes the sprint in 4.6 seconds. However, its average fuel consumption is just 9.1 liters per 100 kilometers (25.85 US mpg), corresponding to 213 grams CO2 per kilometer (342.79 g/mile). The same figures for the A8 L are 9.2 liters and 216 grams (25.57 US mpg and 347.62 g/mile).
These top values are attributable to an entire package of detailed improvements. The most important efficiency technology, however, is the cylinder on demand (COD) system. It shuts down four cylinder under part load by closing the valves and deactivating both injection and ignition. To compensate for intrusive noise, the Active Noise Cancellation (ANC) broadcasts a precise antiphase sound to the cabin, and active engine mounts dampen vibrations during four-cylinder operation.
The high-tech character of the 4.0 TFSI is manifested in numerous details, such as the twin-scroll turbo chargers that provide for the early and rapid development of torque, in the innovative thermal management and in the layout of the cylinder heads. Their intake side is on the outside and the exhaust side on the inside. The turbos and their intercooler are located in the inner V. This layout results in short gas flow paths with minimal flow losses and spontaneous response.
The 3.0 TDI: The efficiency diesel
155 grams CO2 per kilometer (249.45 g/mile), corresponding to 5.9 liters of fuel per 100 kilometers (39.87 US mpg): the 3.0 TDI is a highly efficient engine. The 2,967 cc V6 diesel produces 190 kW (258 hp), 6 kW (8 hp) more than before and generates 580 Nm (427.79 lb-ft) of torque between 1,750 and 2,500 rpm. The standard sprint takes 5.9 seconds with the A8 and two-tenths of a second longer with the A8 L. Fuel consumption is 5.9 liters per 100 kilometers (39.87 US mpg), corresponding to 155 grams CO2 per kilometer (249.45 g/mile). The same figures for the A8 L are 6.0 liters and 158 grams (39.20 US mpg and 254.28 g/mile).
Special technical features of the six-cylinder unit, which underwent a series of modifications, include the low weight of less than 200 kilograms (440.92 lb) and the particularly sophisticated thermal management. The crankcase and cylinder heads have separate coolant loops. Coolant is not circulated in the block during the warmup phase. The 3.0 TDI complies with the exhaust limits of the American ULEV 2 BIN5 specification and also the second stage of the Euro 6 standard, which does not enter into force until 2017.
The 4.2 TDI: Immense torque
The 4.2 TDI tops all of the engines when it comes to torque. The V8 displaces 4,134 cc and produces 850 Nm (626.93 lb-ft) of torque between 2,000 and 2,750 rpm. Its output has increased by a 25 kW (34 hp) to 283 kW (385 hp). The power diesel provides for impressive performance. The sprint from 0 to 100 km/h takes just 4.7 seconds (A8 L: 4.9 seconds). The new Audi A8 4.2 TDI gets by on just 7.4 liters/100 kilometers (31.79 US mpg), corresponding to CO2 emissions of 194 g/km (312.21 g/mile). These values for the long-wheelbase version are 7.5 liters and 197 grams (31.36 US mpg and 317.04 g/mile).
The technical update undergone by the 4.2 TDI included changes to the valve drive, the pistons and the turbocharger. The engineers were able to dramatically reduce the engine speed of the V8 diesel to 800 rpm for improved fuel efficiency. Another aspect in common is the SCR emissions control system (SCR = selective catalytic reduction), in which the additive AdBlue breaks down the nitrogen oxides.
A metering pump injects small amounts of this additive from two tanks with a combined volume of 27 liters (7.13 US gallons) into the special DeNox catalytic converter at the end of the exhaust system. This measure enables the 4.2 TDI to meet the EU 6 emissions standard.
Power transmission
The A8 engine variants roll off the assembly line with an eight-speed tiptronic. The lower gears of the classic torque converter transmission are tightly spaced for sporty performance, while their high overall gear ratio of 7.0:1 reduces fuel consumption. All gear changes are fast, very flexible and smooth. The highly efficient oil pump and the heating of the transmission by the engine coolant during the warmup phase contribute to the high efficiency of the eight-speed tiptronic. A hydraulic accumulator enables the start-stop function.
The Dynamic Shift Program DSP is responsible for controlling the transmission and features the automatic operating modes D and S. It is networked with the route data provided by the MMI navigation plus. The driver operates the eight-speed tiptronic purely electronically, either with the standard shift paddles behind the steering wheel or via the elegant lever on the center tunnel console. A brief tap initiates gear changes.
The standard quattro permanent all-wheel drive (not with A8 hybrid) moves the new A8 to the front of the luxury segment. Its asymmetric and dynamic setup harmonizes perfectly with the sporty and stable handling. During normal driving, the self-locking center differential sends 60 percent of the power to the rear axle and 40 percent to the front. If one axle slips, the majority of the power goes to the other axle. The rear axle differential in the quattro drivetrain helps to balance the distribution of axle loads.
Customers seeking even more dynamic handling can order the optional sport differential for the rear axle. It is standard in the A8 4.2 TDI and the S8. It uses two superposition gears to steplessly vary the distribution of the power between the wheels. In fast curves, the sport differential literally pushes the sedan into the radius. The driver can vary the function of the Audi drive select system in five steps (auto, dynamic, comfort, individual and efficiency).