AUDI Australia has increased the engine choice and lowered the price of entry to its all-alloy A8 luxury limo range with the introduction of two diesel variants alongside its petrol V8.

All engines are now also available with the long-wheelbase option for the first time in Audi’s all-alloy flagship range that now opens at $188,000 for the 3.0-litre TDI base model.

The new 4.2-litre diesel V8 and the similar-sized petrol V8 that was launched with the new-generation A8 in mid 2010 are now both $234,500 – an increase of $8600 for the petrol.

Available with only the 3.0-litre diesel in the previous-generation A8, a 130mm longer wheelbase version that provides greater rear seat space and luxury – including electric rear blinds, vanity mirrors and heated seats on V8 models – is now offered with all engine choices for an extra $11,900 on the V6 and $14,700 for the V8s.

Audi says the arrival of stretched A8s helps level the playing field in the top-end German limo sector and is vital for competing in the fleet limousine market.

The Ingoldstat-based manufacturer claims the short wheelbase 3.0-litre entry-level variant consumes an average of just 6.6 litres of diesel per 100km and can haul its 1840kg mass from standstill to 100km/h in 6.1 seconds before topping out at a governed 250km/h. With a CO2 rating of 176g/km icing the cake, these are class-leading figures.

The closest spec-sheet competitor is the also aluminium-bodied Jaguar XJ diesel, which despite being 44kg lighter, bettering the A8’s peak power by 18kW and its torque output by 50Nm, reaches the 100km/h benchmark three tenths of a second later and produces eight more grams of CO2 per kilometre. The big Jaguar is also $18,800 more expensive.

In fact, Audi’s flagship undercuts its least expensive rival, the BMW 730d, by $14,600 – enough change to buy a new Micra, tick a few option boxes or pay for most of the $16,950 Bang & Olufsen sound system upgrade.

On the other hand, for customers who want to buy a car that has no direct competitor, Audi now offers an update to the twin-turbo diesel V8 that powered half of all Australian-delivered A8s before the previous model was discontinued.

Offering a higher standard specification than the V6 and packing Audi’s tweaked 4.2-litre diesel engine, which made its Australian debut last September in the Q7 SUV, the 1995kg flagship diesel delivers a whopping 800Nm of torque to the road through its Quattro drivetrain.

With 258kW on tap, the sprint to 100km/h is dispatched in 5.5 seconds. Although the petrol V8 reaches 100km/h half a second quicker, real-world, mid-range performance of the diesel is higher.

Owners of the V8 diesel can warm their tyres without warming the planet, as the performance is achieved while generating 199g/km of CO2 and consuming 7.6l/100km. To put this into perspective, an automatic petrol Ford Focus emits 194g/km and returns 8.2l/100km.

The 4.2 TDI’s nearest equivalent, in that it offers green credentials and all-wheel drive, is the $243,814 Lexus 600hL eco-barge but even with hybrid technology, it falls well short of the Audi’s CO2, fuel consumption and performance figures.

Other than the petrol-electric Lexus, luxury V8 diesel options are limited to Range Rover and Audi Q7 SUVs.

The 4.2 petrol’s price increase helps Audi Australia offer the 4.2 diesel A8 at the same price with an equal specification, absorbing the 2000 Euro spec-for-spec price difference that exists in Europe.

For the time being, the V8s represent Audi’s flagship models and there are no plans to import the W12-engined variant to Australia. However, the S8 – rumoured to pack a twin-turbo petrol V8 – is likely to make it Down Under.

The latest A8’s 3.0 TDI’s fuel consumption is reduced by up to 22 per cent over the equivalent previous-generation A8. Apart from being redesigned from the ground up to improve manufacturing tolerances and reduce internal friction, additional fuel-saving touches such as idle-stop, deceleration energy recuperation and a water-cooled alternator (which Audi says reduces fuel consumption by 0.1l/100km alone) are applied.

Thermal management ensures that friction losses are minimised after a cold start by disconnecting the engine from its cooling system to ensure the lubricating oil warms up quickly, then once the engine coolant is hot enough, using it (via a heat exchanger) to warm the transmission oil.

The standard eight-speed ZF automatic transmission also contributes heavily to fuel savings, with its low internal friction and wide spread of ratios providing a six per cent reduction in consumption while improving acceleration.

Audi claims that the A8 is the sportiest car in its class and fits a sport differential, which dynamically distributes forces between rear wheels, as standard on the 4.2 TDI.

The special diff, which is reinforced to withstand the diesel V8’s considerable force, directs torque to the outside wheel in a bend and can react in just 100 milliseconds, making it quicker than the electronic stability control.

All A8s come with plenty of standard kit including pre-sense (which readies the car for impact when it senses an inevitable collision), drive select (which offers custom settings for ride comfort, steering, gearbox and throttle response), keyless entry and start, cruise control, automatically dimming, folding and memory mirrors, 22-way power front seats, leather upholstery, Bluetooth, iPod interface and Audi's MMI infotainment menu system.

The 3.0-litre base model gets 18-inch alloys and relegates the 4.2’s standard 19-inch alloys, ambient internal lighting, adaptive headlights, automatic boot lid, soft-closing doors, Bose surround sound and digital TV to the options list.

Other notable options available across the range include full LED headlights (the lighting elements of which are designed to last the life of the car) for $2700, radar-based adaptive cruise control at $5495, heated and ventilated massage front seats for $5500, individual electrically-adjusted rear seats (deleting the centre seat) at $9440 a rear entertainment package at $9845, two levels of extended leather trim costing $5665 or $20,090 and a “Balao brown” leather, wood and aluminium interior trim package at $26,385 on top of the mandatory $20,090 extended leather package.

Since its launch last year, the A8 has picked up a couple of awards. It scored well in the areas of safety and fuel efficiency and received high praise for its environmental and social acceptability to win the 2010 Golden Steering Wheel award in the Luxury Cars category.

Audi also received top honours from a panel of 520 experts from 22 countries and a jury of specialists in the Euro Car Body Award for the A8’s aluminium bodywork. The award takes into account several factors including the body’s stiffness to weight ratio, production processes, manufacturing techniques, crash-test results, aerodynamic and acoustic properties, and ease of repair.

Almost 10 per cent of Audi's record-breaking January sales volume in Australia was attributed to sales of the new A1, which with 146 units comprehensively outsold its Mini (112), Alfa MiTo (26) and Citroen DS3 (17) competitors.

Diesel engined models account for 35 per cent of Audis sold in Australia and once the A1 receives a 1.6-litre TDI engine mid-year, every Audi except the R8 supercar will be offered with at least one diesel option.