28 February 2005

The new audi RS4: a hi-tech naturally aspirated V8, lightweight body, rear-biased four-wheel-drive system, aluminium suspension and 0-62mph in under five seconds. BMW’s M3 could be in real trouble.

The 414bhp 4.2-litre RS4, which makes its debut at this week’s Geneva show, marks a new era at Audi. For the first time in almost two decades, the German car maker has forgone turbocharging in favour of a highly strung naturally aspirated engine to achieve high-end performance – a move Ingolstadt insiders say will be repeated in a series of exciting new fast Audis, including a new RS6, a storming RS8 and the eagerly anticipated production version of the stunning Le Mans concept supercar.

First of a new breed

The adoption of a naturally aspirated engine for the second-generation RS4 is, however, just one component in a much broader engineering program instigated by Audi’s increasingly active Quattro division, which is desperate to earn the respect paid to its performance rival, BMW’s M-division.

The new 155mph sporting saloon (an estate will follow) also receives a re-engineered four-wheel-drive system, which will apportion power with a 40:60 rear bias, lightweight body panels, aluminium intensive suspension and a reworked driver-focused interior.

Together, the changes are claimed to make the new four-door a much more engaging car to drive than its 380bhp twin-turbocharged 2.7-litre V6 predecessor, and a car that, on paper at least, looks more than capable of standing comparison with the standard-setting a M3.

The RS4 reaches the UK this autumn priced around £50,000.

Design & engineering

Building on the sharpened appearance of the facelifted S4 launched this month, Ingolstadt’s latest supersaloon gains an added dose of visual muscle that instantly differentiates it from its lesser sibling. A deeper front bumper with larger air ducts and distinctive vertical gills on the outer edges, a new plastic honeycomb insert for the single-frame grille and beefed-up front wings dominate the front view, while the sides are characterised by widened sills, signature matt aluminium exterior mirror housings and towering 18-inch double-spoke alloy wheels shod with 255/40 profile tyres. The rear features a small spoiler, deeper valance panel and a pair of large chrome tailpipes.

The new car sits a considerable 30mm lower than the S4 and its overall stance is improved by tracks extended by 37mm up front and 47mm at the rear.

Aerodynamic requirements have influenced changes underneath, where a flat undertray and diffuser provide a more efficient flow of air, while small ducts are employed to cool the engine and brakes more effectively.

Audi has also used its expertise in lightweight construction to keep weight down. The body is made predominantly from high-tensile steel – as with the S4 – but the bonnet and heavily flared front wings are aluminium. At 1650kg, the new car tips the scales a creditable 10kg under the S4 but is 155kg heavier than an M3.

Although Audi has only revealed a saloon version of the RS4, an estate model exists. However, it probably won’t be unveiled until the Frankfurt Motor Show in September.

Engine & transmission

The big news under the skin is the arrival of a naturally aspirated engine derived from the S4’s compact 90-degree V8. The technical details revealed so far indicate very different characteristics to Audi’s earlier turbocharged engines, with sharper throttle response and a more highly strung nature that should make it a hit with enthusiasts.

With a capacity of 4163cc, the engine gets a host of tweaks, including Audi’s FSI (fuel stratified direction injection) system that’s conducive to high revs – the electronic cut-out is at 8250rpm. Peak power is 414bhp – 70bhp more than the S4 and (crucially given Audi’s quest to top BMW) 75bhp up on the existing M3, although the replacement M3 due in 2007 will close that gap courtesy of a 400bhp V8. The RS4’s maximum torque of 317lb ft arrives at a relatively high 5500rpm, although 285lb ft of it is developed between 2250rpm and 7600rpm, which should mean a highly flexible delivery.

A more reliable performance indicator is the RS4’s power-to-weight ratio – at 251bhp per tonne, it makes the M3’s 215bhp per tonne look a little tame.

A six-speed manual gearbox channels drive through a twin-plate clutch and heavily reworked version of Audi’s quattro four-wheel-drive system. In a bid to provide the RS4 with a more entertaining feel, the characteristics of the quattro system have been heavily revised. Instead of delivering drive in a classic 50:50 front-to-rear arrangement, the new system doles out a rear-biased 40:60 split. Insiders admit there is a slight trade-off in traction, but it is a drawback they are prepared to absorb in return for improved poise and balance.

Performance

The RS4 is spectacularly fast by four-door standards. The headline figure is 0-62mph in a claimed 4.8sec – 0.8sec faster than the S4 and 0.4sec inside the M3’s official figure. Those who have experienced the new car’s standing-start acceleration say it lacks the neck-straining take-off of its predecessor’s, although this is compensated for by greater mid-range shove.

Top speed is a limited 155mph, although without intervention the RS4 would haul close to 180mph at the 8250rpm cut-out in sixth gear.

Chassis, steering & brakes

Allied to the RS4’s new four-wheel-drive system is the heavily reworked suspension. The fundamentals are the same as in the S4 – a four-link arrangement up front and multi-links at the rear – but Audi says they have be altered to take advantage of the added drive being put through the rear wheels. The wider front and rear tracks provide greater high-speed stability.

A major development is DRC (dynamic ride control), which uses variable-rate dampers to automatically alter the ride characteristics. The power-assisted rack-and-pinion steering is also more direct than the S4’s.

The RS4 gets the latest ESP (electronic stability program) from Bosch. It gains a higher threshold, permits greater levels of slip and cycles in shorter bursts to provide what insiders describe as more predictable on-the-limit behaviour.

The brakes, too, have been upgraded to cope with the performance. The ventilated and cross-drilled steel discs measure an impressive 365mm in diameter up front and 324mm at the rear.

Interior & equipment

The RS4 is no stripped-out road racer, its cabin builds on the S4’s with a sumptuous combination of leather, aluminium and carbonfibre-effect trim. The steering wheel has been resized and the front seats replaced by hulking hard-shell items that promise massive support.

Interior accommodation is as per the S4, meaning generous space for four adults and 460 litres of boot space. Although high standard equipment levels are promised, items such as satellite navigation and adaptive headlamps will be optional.

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