As well as featuring a cylinder-on-demand arrangement that shuts off four of the eight cylinders on light throttle loads for added fuel efficiency, the engine showcased in the Prologue also uses a 48-volt electrical system – a development that Audi insiders indicate will be adopted on the next A8 and the A9 as part of a new generation of fuel saving initiatives.
The new 48-volt electrical system employs a belt starter generator, which provides the advanced V8 with mild hybrid capability and an energy recovery output of up to 12kW under braking.
So configured, Audi suggests that the production version of the Prologue will return nearly 33.0mpg on the combined fuel economy cycle to give it average CO2 emissions of under 200g/km.
Initial impressions? Well, the big Audi has all the typical hallmarks of a concept car. A lack of ride height means approaching a driveway at anything more than walking pace would risk ripping off the expensive-looking polished carbonfibre splitter attached to the leading edge of the front bumper. So I gingerly manoeuvre out of the hotel, being careful to angle the nose of the Prologue out on to the road to avoid any cringeworthy scrapes.
An exploratory prod on the accelerator reveals that engine response is a little tardy at low revs, due to excess engine bay heat that, Audi engineers say, has caused the electronic throttle mapping to intermittently retard the ignition.
Once I’ve negotiated my way through an initial dead spot in the delivery, though, the turbochargers spool up and the sharp-looking concept smoothly builds up speed.
The Prologue rides on a heavily modified platform from the current A8, although such is the extent of the changes that it is virtually a new structure – one that provides solid clues to the underpinnings set to be used by the next-generation A8 and the A9.
As well as reducing the wheelbase by 50mm to 2940mm, Audi has also provided its latest concept car with a thoroughly new five-link rear multi-link suspension sporting adaptive air springs capable of varying the ride height.
In a more significant move, it also receives a four-wheel steering system that allows the rear wheels to turn by up to five degrees for improved manoeuvrability around town and greater agility on the open road.
For the new Audi’s unveiling, the advanced suspension has been lowered quite significantly in the name of style, robbing the Prologue of any meaningful wheel travel. And those custom 22-inch wheels are shod with purposeful 285/30 Pirelli P Zero tyres offering little in the way of additional compliancy.
Predictably, there is some sharp vertical pitching as we turn right at the traffic lights and set off down Rodeo Drive to the stares of onlookers.
But, wow, there’s encouraging feel and accurate action to the steering. Like many other aspects of the mechanical package used by the Prologue, the electro-mechanical system is taken directly from the S8. It is allied to the new rear steer mechanism that helps to provide the big coupé with an outstanding turning circle of just 8.5 metres – less than that of the significantly smaller A3, or so says Audi.
The Prologue may be a concept, but there is real substance to its low-speed manoeuvrability. Even at limited speeds, it possesses the makings of a very appealing production car. It steers in a direct manner, changes direction eagerly and corners in a flat and unperturbed way.