AUDI has released a topless version of its S5 performance coupe, with a fabric roof that falls in 15 seconds, erects again in 17s flat, and can do it while travelling up to 50km/h.

But while the hardtop version uses a 260kW/440Nm 4.2-litre FSI V8 petrol engine, the S5 Cabriolet – on sale now from $138,100 – ditches two cylinders for a supercharged TFSI V6 unit. We expect the S5 Coupe to follow suit sometime towards the end of next year when the range receives a midlife makeover.

This single move makes for a 24 per cent fall in fuel consumption.

Driving all four wheels via Audi’s Torsen differential quattro all-wheel drive system, this 2995cc 3.0-litre V6 engine has a power peak of 245kW between 5500rpm and 7000rpm and 440Nm of torque from 2900rpm and 5300 rpm.

In normal driving conditions torque is rear-biased 60/40, with the back wheels capable of handling as much as 85 per cent while the fronts are limited to 65 per cent.

The only gearbox on offer for the time being is a seven-speed S-tronic dual-clutch system with paddle shifters that Audi used to refer to as a DSG transmission. The S5 Cabriolet joins an increasing number of models to marry S-tronic with a longitudinal drivetrain application.

The Ingolstadt company claims the four-seater ragtop races from zero to 100km/h in 5.6 seconds, on its way to an electronically limited 250km/h. Conversely it returns 9.7 litres per 100km and has a carbon dioxide emissions footprint of 227 grams per kilometre.

Central to the S5 Cabriolet’s performance is a new supercharger application, sited in the space between the two banks of cylinders to pressurise the direct-injection V6 to up to 0.8 bar. Audi says two downstream intercoolers reduce the temperature of the compressed intake air.

Like all of Audi’s B8-series based models, this car employs the MLB (Modulare Längsbaukasten) architecture, which sees the front wheels pushed further forward than in previous longitudinally engined models to create a more favourable front-to-rear weight balance.

Suspension is via a five-link front-end design and a trapezoidal-link rear end set-up, and is in a sports state of tune (lower and stiffer) to differentiate the S5 Cabriolet from the regular A5 Cabriolet introduced in August.

Steering is by speed-sensitive Servotronic rack-and-pinion.

Design-wise, the S5 Cabriolet differs from the A5 soft top by its revised bumpers, front spoiler, rear diffuser and sill trims, four exhaust pipes, aluminium exterior mirror casings and unique alloy wheels.

The latter are 18-inch cast aluminium items shod with 245/40 tyres.

One of the S5 Cabriolet’s unique selling points is its split fold rear seat arrangement, resulting in the 320-litre luggage capacity growing to 750 litres thanks to the 1.76 metre available floor space.

Standard features in this four-seater convertible include tyre pressure monitors, Alcantara leather trim, Audi’s MMI Navigation Plus, Xenon Plus high intensity discharge headlights, LED daytime driving lights, a keyless entry and start system, electric and heated front seats, cruise control, parking radar and an electrically operated soft top with the company’s ‘acoustic’ sound deadening material (14mm of extra foam).

Audi is also offering its ‘Drive Select’ option, which in a special rear-wheel differential for left-to-right torque split capability, as well as adaptive dampers and a ‘Dynamic Steering’ feature that alters the tiller’s responsiveness, for $6900 on top of the $138,100 asking price.

Around 100 units are forecast to find homes in 2010, making up about 20 per cent of A5 Cabriolet sales. The other models – the A5 Cabrio 2.0TFSI, 3.0 V6 TDI and 3.2 V6 FSI – are expected to make up the remaining 40, 30 and 10 per cent respectively.

The S5 Cabriolet serves as a replacement for the B7 A4-based S4 Cabriolet sold in Australia from April 2005 to January 2008.

Also a quattro AWD, that car used a 253kW/410Nm 4.2-litre V8 mated to a six-speed Tiptronic automatic gearbox.