Variable-displacement Audi A3 here soon

Audi’s new A3 Sportback will be launched in Australia next week, but in October the company will follow the initial petrol and TDI offerings – two of each – with a second version of the 1.4 TFSI bringing cylinder-deactivation technology into the four-cylinder market.

Good for 103kW and serving up its 250Nm peak torque between 1500 and 3500rpm, the COD engine is more potent than its 90kW/200Nm conventional stablemate.

Audi Australia hasn’t yet released local fuel consumption and emission figures, but in the UK it’s rated at 60.1mpg or 4.7L/100km combined, against the conventional 1.4 TFSI’s 54.3mpg or 5.2L/100km, and 109g/km against 120g/km CO2.

That means a win-win – 14 per cent up on power, 25 per cent up on torque with a 10 per cent improvement in fuel economy and emissions. While it’s too early for the company to announce local pricing, in the UK A3 the package commands an £850 premium (about $1300) over the normal 1.4-litre four.

Asked if this is any indicator of the local mark-up over the conventional engine, Audi Australia spokeswoman Anna Burgdorf told motoring.com.au it’s too early to tell.

“We haven’t even finalised it yet, but in any case it’s way too early to announce it, given it’ll be October at the earliest that we see it here,” she said.

“Given benefits it confers in power and economy, we’ll obviously be asking something extra for it. But there are too many variables to factor in between here and overseas markets to say whether it’ll be more or less.”

The cylinder-on-demand (COD) system knocks the two middle cylinders out of the combustion cycle under low to moderate load, compensating with a slight shift to the timing on the two cylinders still running.

It’s a variation of the system Audi introduced in this year’s 4.0-litre V8 S6 and S7 models, using the variable valve-timing principle that changes engine behaviour by shifting the camshaft sideways to a second set of teeth, activating a new timing sequence.

On a signal from its sensors, the on-demand system shifts the cam to bypass cylinders two and three, leaving the valves closed and shutting down the fuel injectors. When the system’s sensors detect a rise in demand for power, the cam clicks back to normal and reboots the passive pistons.

Audi says on/off operation takes anywhere from 13 to 36 milliseconds, depending on engine speed. Compensatory help from fuel-injection, ignition timing and the throttle valve make cutover barely if at all perceptible.

Modifications to the engine mounts, flywheel and exhaust system help keep two-cylinder NVH to virtually zero. (In the V8 they take this a step further, with active engine mounts that smooth out the hollows in the firing sequence in V4 mode, and an electronic noise-cancelling system in the audio package.)

Audi says it’s so smooth that without the indicator in the instantaneous fuel economy display, drivers would be hard pressed to tell whether it’s running on two or four pots. In third gear, it cuts in from about 30km/h, pulling out from about 130km/h in fifth and sixth.

It’s capable of predicting when it’s not worth the effort, too. When driving patterns become too dynamic for it to effect any real fuel savings, for example traversing roundabouts or getting a bit of stick along on a decent stretch of back road, it disables COD altogether until things stabilise.

Cylinder deactivation isn’t new, although to date it’s been largely restricted to sixes and V8s. The only other manufacturer to try it on a four is Mitsubishi, which had a crack at it in the early 1980s and again a decade later.

The Japanese maker offered a “modulated displacement” version of the 1.4-litre four it was putting in 1980s Colt, Lancer and Cordia models in some markets.

With buyers failing to see the point, it killed it off within a year or two. At least until the early 1990s, when it brought it back with its new MIVEC variable valve timing. Buyer apathy reigned again, and it was discontinued in 1996.

Cylinder deactivation can be found in Australia in Holden’s Active Fuel Management (AFM) V8/4, Chrysler’s V8/4 300C and Honda’s three-phase Variable Cylinder Management (VCM) Accord V6/4/3.

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