A8 4.0 Tdi Monster
Date: Friday, May 16, 2003 @ 05:58:39 BST
Author: audioc
Topic: A8, S8

275 bhp, 650 Newton metres- the Audi A8 4.0 TDI quattro

Audi is expanding the range of engines available for the A8 to include a third and, once again, emphatically sporty version: a newly developed V8 TDI. The A8 4.0 TDI quattro, which develops 202 kW (275 bhp) and 650 Newton metres of torque, is the world’s most powerful eight-cylinder diesel engine in a production saloon car.



With its compelling handling, pioneering technology and distinctly exclusive design and equipment, the new Audi A8 has distinguished itself as the epitome of sportiness in the luxury segment since it was launched in autumn 2002. This also applies to the new version with four-litre V8 engine. As the sportiest diesel saloon car on the market, the A8 4.0 TDI quattro unites technical characteristics that set it clearly apart from the rest of its class. And as the brand flagship, the 4.0 TDI, like the other A8 versions, embodies the characteristics of the future Audi generation through sporting dynamism and clear design, innovative technology and top quality.

The newly developed biturbo V8 with two intercoolers not only has a higher swept volume and power output than its predecessor, the 3.3-litre 165 kW (225 bhp) engine; it is the first TDI version in Audi's new range of V?engines and has a chain drive for camshafts and ancillaries.

The A8 4.0 TDI quattro puts up the performance of a top athlete. This fleet-footed luxury saloon with aluminium body sprints from 0 to 100 km/h in just 6.7 seconds – faster than any other diesel saloon car worldwide. It reaches a governed top speed of 250 km/h. And its torque of 650 Newton metres offers a quality of traction across the entire road-speed range that can otherwise only be experienced in sports cars.

650 Newton metres between 1800 and 2500 rpm not only make the A8 4.0 TDI quattro the highest-torque Audi in existence, but also put it right at the top of its class. The 4.0 TDI engine is currently the highest-powered, highest-torque V8 diesel engine in any production saloon car. Its impressive refinement moreover sets a new benchmark in this class.

Compact power plant

Following in the footsteps of the 4.2-litre petrol engines which power the Audi S4 and the allroad quattro 4.2, the 4.0 TDI is now the third member of Audi's new family of V-engines. The TDI, too, is remarkable for its very compact dimensions: the engine measures just 516 millimetres in length. By way of comparison: one particular new V8 engine built by a competitor is almost 150 millimetres longer, even though its displacement is the same.

The 90-degree engine block of the V8 is made from vermicular graphite cast iron, a material that exhibits almost twice the strength of conventional grey cast iron yet weighs around 15 percent less. This is one of the vital clues to the engine's low overall weight of just 270 kilograms, which makes the 4.0 TDI one of the lightest diesel V8s around. This benefits both the power-to-weight ratio and weight distribution equally – two parameters that are of central importance for the driving dynamics of the new A8 4.0 TDI quattro.

Both the bore (now 81.0 mm) and the stroke (now 95.5 mm) are larger than on the predecessor version. This results in an overall displacement of 3936 cc. The cylinder spacing is unchanged at 88 millimetres. The compression ratio has been reduced from 18.5 : 1 for the 3.3 TDI to 17.5 : 1 on this version.

There are four valves per cylinder, for optimum charging of the combustion chamber. The valves on the new V8 are operated by roller cam followers with hydraulic valve clearance compensation, whereas the earlier version still used sliding cam followers. This low-friction drive technique plays a decisive part in reducing both the fuel consumption and the emissions of the 4.0-litre engine.

The use of roller cam followers is likewise beneficial to the engine's acoustics. In conjunction with the twisted-type and therefore virtually play-free camshaft drive, these followers are instrumental to the reduction in mechanical noise from the valve gear and contribute to the 4.0 TDI's outstanding smooth running.

The rigid construction of the engine block and the unit’s effective encapsulation also help to lessen the sound emitted by the eight-cylinder engine. Smooth combustion brought about by the optimised pilot injection of the latest-generation common rail system makes a further – and decisive – contribution to the engine’s extremely refined acoustics.

New common rail technology

The newly developed Bosch EDC16 system, with fuel delivery, injection-start, boost pressure and exhaust-gas recirculation control, is responsible for engine management in the V8 TDI.

As on the A8 with V8 petrol engine, this electronic system now means that it is possible to start the engine automatically at the push of a button. The preheating system ensures that it takes no more than a few moments for the engine to spring into action, even at low winter temperatures.

Mixture preparation is performed by a second-generation common rail system with one high-pressure pump and one rail per cylinder bank. On the new generation of engines, the injection pressure has been raised from 1350 bar to a maximum 1600 bar. 1600 bar is equivalent to the weight of a midsize saloon car being supported on an area the size of a finger nail.

This high injection pressure results in even finer atomisation of the fuel and therefore in better mixture preparation and more efficient combustion. The consequence is not merely extra power and torque, but also reduced fuel consumption and emissions.

The second-generation solenoid-valve injectors with 7-hole nozzles are also new. They, too, play a major part in making the combustion process ultra-efficient, and thus improving the quality of emissions, by distributing the fuel homogeneously throughout the combustion chamber.

The result is that even though the Audi A8 4.0 TDI quattro - unlike its competitors - has permanent four-wheel drive, it clearly undercuts the limit values specified in the EU III standard thanks to its low untreated emissions.

What is more, the new common rail system is capable of injecting fuel several times per combustion cycle. Double pilot injection takes place at low engine speeds, single pilot injection in the medium speed range. This strategy produces a smoother combustion process, the benefits of which are most immediately apparent in the engine's acoustic behaviour. The 4.0 TDI engine is not only much quieter and smoother-running than its predecessor, it now unquestionably serves as the benchmark in its class.

Biturbo with two intercoolers

A concept that has already proven its worth on the 3.3 TDI engine: two turbochargers with variable turbine geometry develop high torque even at low engine speeds, in conjunction with a high power output. Variable turbine geometry means that the flow of exhaust gas to the turbine wheel can be optimised depending on load and engine speed. By means of air mass metering, the engine management ensures that both turbochargers run constantly at the same speed and therefore achieve the same delivery rate. Maximum boost pressure is 2.2 bar; the turbochargers rotate at up to 210,000 revolutions per minute.

The variable turbine geometry is supported by electrically operated actuators on the new 4.0 TDI. These actuators adjust the vanes faster and with greater exactitude. Particularly at low engine speeds, this builds up the boost pressure faster and thus achieves a significantly better response. The dreaded problem of "turbo lag" is an utterly alien concept on this engine.

Another new feature on the 4.0 TDI is that there are two air-to-air intercoolers, arranged on the right and left in front of the engine. They are ideally positioned in the airflow beneath the headlights, and are therefore capable of operating extremely efficiently.

Each of the two turbochargers serves one bank of cylinders. The two intake manifolds are interconnected by means of a "feedthrough" system, to equalise the pressure between the right and left cylinder banks. This feature boosts cylinder charging and consequently enhances the engine's output.

There are variable, two-position swirl flaps integrated into the intake tract which can be used to adjust the air movement according to the prevailing engine speed and load. High swirlat a low engine load optimises the combustion process as, conversely, does low swirl at a high engine load. In practice this means that a closed swirl duct at low load increases swirl, while open ducts at high load boost cylinder charging.

Efficient emission control

To minimise thermal losses from the exhaust gas before it reaches the turbocharger, the exhaust manifold is of double-walled design, in other words it has air-gap insulation. Exhaust gas recirculation, on the other hand, requires efficient cooling, in particular in order to reduce NOx and particle emissions effectively.

The gas is cooled in two water-type exhaust-gas recirculation radiators inside the engine's "vee", an arrangement which contributes towards the engine's efficient use of space.

The exhaust gas is purified by two close-coupled primary catalytic converters – located close to the turbochargers – and the main converters under the floor. As a result of all these measures, the A8 4.0 TDI – equipped with quattro drive and 6?speed automatic transmission – easily undercuts the limit values of the EU III standard.

Consumption reduced

One feature of the new engine that is undoubtedly as welcome as its ecological efficiency is its impressive fuel economy. In remarkable contrast to the shift in its power and torque curves, its fuel consumption has actually been reduced. It averages a mere 9.6 litres of diesel fuel per 100 kilometres – a figure that is even below the already economical value for the old A8 3.3 TDI quattro, despite the fact that its power output is 50 bhp higher and this vehicle weighs more overall.

It therefore comes as no surprise to learn that the new A8 4.0 TDI quattro has an operating range that singles out this luxury saloon as the perfect long-distance vehicle: it can cover almost 940 kilometres on a single tank of fuel.

Not only do drivers of the A8 4.0 TDI make rare stops for fuel, they do not have to bring their vehicle in for servicing very often either. The V8 diesel version also benefits from extended service intervals, with a service indicator in the instrument cluster. Intervals of up to two years or a maximum of 30,000 kilometres are possible, depending on driving style and conditions.

A8 4.0 TDI quattro: supreme sportiness in the luxury segment

The new 6-speed tiptronic with Dynamic Shift Program DSP and additional Sport program is available for the first time in conjunction with a TDI engine. Thanks to the extra gear, the engine's output and torque are always unleashed with such precision that the conflicting requirements of spontaneous power flow, high performance and perfectly refined running are all achieved.

The additional sixth speed moreover means that the spread between the lowest and highest ratios has been increased by 30 percent – a vital requirement of greater dynamism on the one hand, and optimum economy on the other.

As an option, it is possible to change gear either using the selector lever in the tiptronic gate or via shift paddles mounted on the steering wheel. The ergonomic advantages of this concept have already been demonstrated on the Le Mans champion model, the Audi R8: drivers can also change gear when cornering, without having to take their hands off the steering wheel.

In conjunction with the low weight of the aluminium body built using the Audi Space Frame principle, the engine and transmission turn in an excellent performance coupled with exemplary economy.

quattro permanent four-wheel drive continues to lead the way in the luxury segment. It converts the engine's performance into superbly effective propulsion and cornering stability, and effortlessly translates the immense torque into locomotion.

The aluminium body: progress through lightness

The innovative aluminium body, based on a refined version of the Audi Space Frame (ASF), provides the high-strength basis for low weight, a dynamic performance and excellent handling. It was possible to considerably reduce the number of components on the continuous ASF compared to the first A8 generation through the use of large functional castings and extruded sections. Static torsional rigidity was increased by 60 percent and ensures a major improvement in vibrational comfort, safety and dynamic handling potential. The body shell weighs 50 percent less than a steel body: minimum mass combined with maximum stability.

The running gear: more dynamism as the driver wishes

The new Audi A8 has a refined aluminium chassis with four-link front suspension and self-tracking trapezoidal-link rear suspension. The brakes and steering system with variable ratio and servotronic are a new design.

Adaptive air suspension – a 4-corner air suspension system with continuous damper control – solves the classic conflict of aims between good handling properties and suspension comfort commensurate with the luxury class. The adaptive air suspension system has the right characteristic for every driving situation, reduces body movements with its continuously adjusted damping and thus optimises roadholding and comfort.

The data from four sensors on the axles and three acceleration sensors on the body is evaluated in the adaptive air suspension's central control unit. This computer prompts the adjustment of the individual shock absorbers in a matter of milliseconds, based on the driving situation identified, thereby always assuring optimum driving dynamics and ride comfort.

The driver can choose between four predefined settings, for a suspension characteristic ranging from overtly sporty to ultra-comfortable.

- In the automatic mode, the body is at the standard height when stationary and at medium speed, with 120 millimetres of ground clearance. If the new A8 is driven at more than 120 km/h for over 30 seconds, the body is lowered by 25 millimetres. In the reverse order, the body is raised if the vehicle is driven more slowly than 70 km/h for more than two minutes or as soon as it drops below a speed of 35 km/h.

- The dynamic mode lowers the vehicle by 20 millimetres to a ground clearance of 100 millimetres even before it sets off; its centre of gravity is lower and the air suspension operates with firmer springs and a harder damping characteristic. The suspension tuning is particularly agile as a result.

- The comfort mode enables the car to glide extra-smoothly over all kinds of surface bumps because the system increases damping forces less frequently at lower speeds. The automatic lowering at motorway speeds is suppressed in order to obtain maximum compression travel.

- The lift mode can be activated in the speed range below 80 km/h as required. It raises ground clearance constantly by 25 millimetres and offers the balanced damping characteristics of the automatic mode. It is therefore particularly suitable for driving on uneven terrain.

The MMI operating concept:
maintaining diversity, reducing complexity


With the integrated user interface MMI, Audi offers an infotainment platform and user concept for the new A8 that keeps operation simple through stringent logic. MMI in the first instance comprises the control panel (MMI terminal) in the centre console with a control button that can be turned and pressed and four control keys grouped around it.

On either side of the terminal – apart from the Return key for exiting the menu level – there are a total of eight function keys with which the user can call up the most important main menus directly. The second central component of the MMI, a 7-inch colour monitor which can be retracted into the instrument panel, is positioned above the centre console in the dashboard and therefore at an optimum angle of view for the driver.

The basic geometry of the monitor display corresponds in detail to the layout of the control keys and button in the MMI terminal. There is thus an intuitive link between visual perception and hand movements. The more frequently a function is used in the car, the higher up the menu structure it is placed, thus making it quicker and easier to access.

Standard equipment

There is no doubt that the exceptional quality of the new Audi A8's standard equipment, as well as its sheer diversity, redefines the standard in the luxury class.

With its ASF-type aluminium body, aluminium chassis, adaptive air suspension, quattro permanent four-wheel drive and 17" wheels on the V8 versions, Audi's new flagship model is undeniably positioned as the most sporty saloon in the exclusive car class.

The A8's steering has speed-dependent and now also steer angle-dependent servotronic. The steering effort required thus varies according to road speed and steering-wheel angle.

The new 6-speed tiptronic, the new leather multifunction steering wheel with 4-spoke design and the optimised deluxe automatic air conditioning with moisture sensor and sun sensor provide maximum comfort and convenience. The boot lid with power-assisted closing and the cruise control system likewise enhance these qualities.

But that is not all. Pioneering technologies such as the MMI Multi Media Interface, battery energy management, the electromechanical parking brake with starting assist function and LED technology in the rear lights and side turn indicators are the best possible proof of Audi's proverbial "Vorsprung durch Technik", exemplifying a competitive edge that extends right up to the luxury class.

Active safety is enhanced by the latest version of the Electronic Stabilisation Program ESP with hydraulic brake assist. The high-performance brake system with 17-inch disc brakes ensures safe and effective deceleration.

A8 drivers have a total of 15 exterior colours to choose from.

Inside the car, the standard-fit audio system provides acoustic quality and up-to-the-minute information. 4-way aerial diversity and a total of eight loudspeakers plus subwoofer ensure excellent reception and sound quality at all seats. An equalizer matched to the car’s equipment and trim specification takes into account changes to interior acoustics caused, for instance, by the choice of cloth or leather upholstery.

Integration into the MMI operating concept has raised the level of operating convenience most impressively. A list of all radio stations that can be received in a given region appears at the touch of a button and is constantly updated by the tuner.

Important optional extras

In recognition of the affinity of many A8 drivers for sporting characteristics throughout the vehicle, Audi offers the option of adaptive air suspension – sport. This sports suspension permits a level of driving dynamics that represents a new dimension in the segment of luxury-class saloons.

The 18 and 19-inch wheels are attractive to look at and optimise road behaviour. The new A8 is the first Audi to be available with wheels with run-flat tyres (PAX system); even when entirely deflated, these tyres remain securely on the rim and afford a hitherto unprecedented level of operating reliability in an emergency. A highly polished 20-inch wheel of 9-spoke design available from quattro GmbH is a new addition to the range.

The radar-controlled adaptive cruise control represents a major advance on conventional cruise control systems. The intelligent convenience system constantly monitors the distance between the car and the preceding vehicle, and adapts the car's own speed accordingly by manipulating the accelerator and brakes. This makes the driver’s task decisively easier.

The adaptive light cornering lights, which Audi first introduced for the A8, noticeably broaden the driver's field of view. Depending on road speed, steering angle and turn indicator signal, the system activates an auxiliary headlight that enlarges the illuminated area sideways – a clear safety gain.

3-spoke leather-covered multifunction sports steering wheels and a wooden sports steering wheel with gearshift function are available in addition to the standard 4-spoke multifunction steering wheel with leather rim. Additional functions, such as the shift paddles mounted on the steering wheel and a heating function, can be ordered as add-on modules.

The optional comfort seats enhance long-distance comfort and sports seats provide extra lateral support. Both have additional scope for electrical adjustment: the upper backrest and thigh support are individually adjustable. The comfort seat can also be supplied with seat heating/ventilation and massage function.

With its several predefined lighting profiles, the interior lighting package with ambient lighting illuminates the interior to suit various situations. In addition, the ambient lighting provides a new level of harmony with the interior design as a whole.

The four-zone deluxe automatic air conditioning allows temperature and air distribution to be adjusted separately for all four seats.

Advanced key permits the driver to open the new A8 without having to take hold of the key. A signal transmitter in the key releases the central locking when the vehicle is approached and allows the engine to be started at the push of the starter button as soon as the key is inside the car.

The one-touch memory personalisation system allows up to four drivers to specify individual presets for a wide range of functions and settings, and to have them activated spontaneously once they themselves have been automatically identified. The system identifies each driver by his or her fingerprint, which is scanned by a sensor pad on the advanced key system's starter button.

A positive comparison with a memorised fingerprint initiates an array of processes: the seats, mirrors and steering wheel are adjusted to the individually preset configuration, together with the air conditioning’s temperature and air distribution settings. The one-touch memory can also activate individual infotainment preferences for the relevant driver.

The market for luxury-class diesel vehicles

For all the scepticism that this concept used to generate, diesel vehicles have now become successful, mainstream members of the luxury car class. Out of around 105,000 German-built luxury saloon cars currently sold each year, 22,600 are diesel-powered. This figure has risen remarkably, and is more than double the 1999 figure, when sales of diesel models in the luxury class reached a mere 9,000.

It remains the case that diesel cars are almost exclusive to Europe. The German market accounts for around 47 percent of the total, with a further 52 percent being exported to other European countries. Only one percent is shipped overseas or to the Far East.

The 4.0 TDI quattro is expected to capture a share of approximately 30 percent of total A8 sales in Germany, and exceed a share of 20 percent in the rest of Europe.

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