We like
Smooth and effortless power delivery, eight-speed automatic transmission, mid-range acceleration, artificial engine note

Room for improvement
Little sensation of acceleration or speed, turbo lag

THAT Audi is not marketing the A6 and A7 TDI Biturbo (BiTDI for short) as a diesel alternative to the petrol V8-powered S6 and S7 perhaps speaks volumes about the lack of emotional connection this ruthlessly efficient new diesel engine provides.

The company has engineered an ingenious artificial solution to the lack of sonorous engine note with speakers in the exhaust and a resonator in the intake, and these are more convincing than other recent efforts by other manufacturers, but to be honest we were left a bit cold.

At GoAuto we are fans of the Audi A6, especially the purity of the four-cylinder entry variants and the instantaneous, neck-snapping sling-shot surge of the supercharged petrol V6 that, on paper, is slower than the new BiTDI – and a whole lot thirstier.

But, aside from a bit of turbo lag, the 230kW/650Nm BiTDI is too refined, too smooth and for some reason builds speed in an infuriatingly imperceptible manner that belies the absolutely astonishing rate the needle travels around the speedometer.

A squeeze of the throttle to overtake a caravan travelling at 80km/h resulted in 140km/h before we knew it, followed by a hard stab on the (potent) brakes in case the police were watching.

We did not feel pinned into our seat – not even during a full-bore standing start to experience 0-100kmh in 5.1 seconds – and the sensation of speed was licence-threateningly absent, so forking out for the head-up display is therefore recommended.

The upside of this engine is relaxed and effortless long-distance cruising, something well demonstrated by our drive route from Canberra to Sydney, and almost peerless overtaking ability for maximum confidence passing rows of slow-moving traffic on country roads.

At urban speeds, with the engine sound set to ‘dynamic’, we enjoyed the baritone burble that takes on an almost V8-like sound when using the engine’s considerable torque to ascend hills in a high gear, but it gets a bit boomy as revs rise and produces an irritating background noise while cruising, so just as well it can be switched off.

Audi has paired the new engine with the smooth and almost seamless eight-speed ZF automatic from the larger A8.

Compared with the seven-speed dual-clutch S tronic transmission on other six-cylinder A6 variants, it dithers a little when asked to kick down.

Compounding this is what seems to be an extra touch of turbo lag as all that extra plumbing pressurises (rather than twin turbos directly connected to the exhaust and intake, there are two different-size units whose interplay is controlled by a valve).

Of course, there is plenty of performance to make up for this perceptible delay, but the lack of instantaneous response takes some getting used to and requires forward planning on twisty sections of road or pulling into a tight traffic gap.

On the subject of twisty roads, the A6 we drove was fitted with the $2245 optional sports differential, which with the Audi Drive Select option set to dynamic mode and all that torque on tap makes for some interesting tail-out action.

Our test car was also fitted with the $1360 sports seats, which were not all that sporty in terms of bolstering, particularly for the torso, but provided great thigh support and were comfortable enough for our long drive.

As with any other A6, we enjoyed the peerless interior quality and design, were a bit disappointed by the lack of steering feel and pleasantly surprised by how far Audi has come in terms of engineering taut body control without compromising ride comfort.

Compared with ridiculously priced options such as the $2280 metallic paint, the Technik option pack (comprising full LED headlights, quad-zone climate control and top-view 360-degree camera display) at $4095 seems like good value.

The top-view camera system is one of the best we have experienced, providing a split-screen layout that shows the reversing camera image and lines to show whether objects can be avoided within the steering arc.

The BiTDI serves a purpose for those who regularly have to overtake road trains, must have the latest technology or are just determined to buy the most expensive A6 or A7 in the range without going for the V8 S models.

For everyone else, the BMW 535d provides the same power and only 20Nm less torque but feels faster, is more fuel-efficient by a meaningful margin and out-handles the Audi, for just $2700 more than the A6 BiTDI.

We are sure the BiTDI is just great on the unrestricted Autobahns of its homeland, but here in Australia it promises more than it delivers.

The buying decision may be further coloured by the fact that, in making way for the BiTDI, Audi recently slashed the price of the standard V6 diesel A6 by $9000 and snipped $7000 off the equivalent A7.

The still-impressive 180kW engine also copped an 80Nm torque output boost, to 580Nm, and the A7 received the BiTDI’s eight-speed auto.

But at this end of the price spectrum, and fuel costs aside, we would still go for the supercharged petrol V6, the price of which was also slashed – by $7000 on the A6 and $3500 on the A7 – while receiving an 8kW power hike to 228kW (torque remains at 440Nm).

We wait with interest to see whether the BiTDI becomes more satisfying when Audi launches its first diesel S model, the SQ5 SUV, later this year.