Diesel is not only about efficiency but also performance. And diesel is fun - it definitely isn't smoky or smelly anymore.

Audi Singapore is hoping that mantra will inspire more prospective buyers than the slinky lines of the elegant A5 coupe.

This stylish two-door model already comes with two petrol engines - 1.8 inline four-cylinder and a 3.2 V6 - but the German luxury carmaker has just added another interesting option - a three-litre V6 diesel.

Press the metal start button on the lower centre console to fire up the engine and the first thing you will notice is that the Audi A5 3.0 TDI quattro is strangely silent.

It sounds just like another petrol-driven car with none of the traditional diesel clatter. Step out of the car and it is still not apparent that it's a diesel unless you put your ear close to the front grille.

The reason is that the A5 engine has Piezo fuel injectors. The injector nozzles allow up to five injection processes per cycle.

With this more precise delivery of fuel, combustion becomes a smoother affair, thus reducing engine noise.

But while the diesel noise has been virtually eliminated, the A5 3.0 TDI still offers diesel's most distinctive feature - its amazing torque.

The 3.0 TDI serves up 500 Newton-metres of torque from just 1,500 rpm. Compare this with the A5 3.2 and its petrol unit's 330 Nm at 3,000 rpm.

From a stationary start, those 500 Nm don't seem too obvious. But the oomph is there when you're on the move and the engine's elasticity is remarkable.

Even as you begin to visualise an overtaking manoeuvre, the A5 3.0 TDI is already performing it. The torque is just bubbling and eagerly waiting to be released by your right foot.

Of course, the delivery of power doesn't feel quite as linear as with a large petrol engine - everything merely arrives in one big punchy package in the 3.0 TDI.

But mated to the smooth six-speed tiptronic auto transmission, it doesn't feel unnatural.

Then there is the brilliant Audi Drive Select driver assistance feature to match the car's setup to your particular driving mood.

In addition to Comfort, Auto or Dynamic modes, the 3.0 TDI also has Individual, which can tailor the throttle and gearbox response, as well as the steering feel and stiffness of the suspension to your specific needs.

And with quattro all-wheel-drive as standard, the A5 has superb adhesion around fast corners. Its levels of grip and control are so high that the A5 is fun yet failsafe.

There is, however, a downside to all this, and it is called the diesel tax. While the petrol-engined A5 3.2 has an annual road tax of $2,693, the A5 3.0 TDI's is $6,055 including the special tax.

Of course, the frugal nature of diesel offers a roughly 30 per cent fuel savings compared to an equivalent gasoline engine. Not to mention the fact that the pump price of diesel is about 55 cents less per litre than regular 98 octane petrol.

So unless you clock up enough mileage and you just can't live without a truckload of torque, the diesel tax can be a deterrent. What a shame.

Audi A5 3.0 TDI quattro

Engine: 2,967cc V6 turbodisel
Transmission: 6-speed tiptronic transmission
Max power: 240 hp @ 4,000-4,400 rpm
Max torque: 500 Nm @ 1,500-3,000 rpm
0-100 kmh: 6.1 secs
Top speed: 250 kmh
Price: $206,800 (with COE)
Distributor: Premium Automobiles
Tel: 6566-1111

This article was first published in The Business Times.