RS4

Courtesy of Edmunds Inside Line

If the engine is the soul of every car, then the 2007 Audi RS 4 has more character under its hood than most performance cars possess from tip to tailpipe. With 4.2 liters of direct-injected aluminum fury, its V8 makes 420 horsepower and 317 pound-feet of torque, and revs to an unbelievable 8,250 rpm.

Now that's some soul. And it's all forward of the front axle.

Defying physics
Any V8, even an aluminum V8, hanging forward of the front axle should do awful things to any car's handling. But in the RS 4, it doesn't.

Just like Porsche, Audi seems to have thwarted both mechanics and inertia with the RS 4. Audi engineers are saddled with this less-than-ideal design constraint in every model utilizing a longitudinal engine layout. Still, we drove it harder than any socially responsible owner ever will, fully expecting a hard lesson in Newtonian physics. It never happened.

The RS 4 is a composed master of winding roads. Confidence and grip from the front tires are superb, balance is good and steering feel, at speed, is better than any Audi we've ever driven. Audi's Servotronic steering increases pressure to the steering rack based on vehicle and steering speed. The ratio is almost Evo quick at 13.1:1 but feels far calmer on the road than the feline reactions of the Mitsubishi. There's something very German about the steering — probably thanks to proprietary bushings that locate the rack. It lacks the texture and resolution of the sharpest systems, but offers more than enough feedback and response during hard cornering to go very, very quickly.

The RS 4's character is very different from, say, a BMW M3, which is lighter. In an M3 the chassis and road connect via the driver. The result is an experience that can only be had with less weight and fewer mechanical interruptions. The RS 4 is probably quicker on most roads, but don't expect M3 levels of involvement from a car that's only 19 pounds shy of two full tons.

With the RS 4, Audi has created a near perfect ride/handling trade-off. Part of the magic is Dynamic Ride Control, which links diagonally opposite front and rear dampers with a gas-charged reservoir. The mechanical system allows more compliance when front and rear dampers are compressed at the same time, ensuring a comfortable highway ride with minimal compromise during performance driving.

The soul
The RS 4's 4.2-liter V8 shares only its bore, stroke, power steering and water pump with the S4 engine. Direct injection mandated new cylinder heads, yielding a 12.5:1 compression ratio. Both the intake and exhaust cams are given 40 degrees of valve timing control.

Pushing the "S" button mounted on the dashboard further excites the RS 4's soul. It quickens throttle response and opens additional valves in the mufflers and intake to allow anyone within earshot to appreciate its 8,250-rpm salute.

Even at low rpm the V8 is eager and provides ample motivation. Ninety percent of the engine's torque is available from 2,250 to 7,600 rpm. This flexible power delivery gives the car its unique character. It's virtually impossible to catch the engine off guard regardless of gear selection, but it never has the brick-to-the-kidneys punch of a large-displacement V8 either.

Wind the V8 to the end of its range and it'll stir your soul with an anthem of German-engineered combustion thunder. The last 2,000 rpm seems to go on forever and makes the RS 4 more flexible than any car in its class. It's Porsche 911 performance with Audi A4 practicality. It will change the way you think about driving fast. Even coming out of slow corners we found ourselves comfortably up a gear from many cars we've driven over the same roads.

Part of that cornering speed is thanks to the RS 4's quattro all-wheel-drive system. Audi updated the RS 4's center differential switching from a viscous unit to a Torsen differential with a 40/60 rear-biased torque split. A six-speed manual transmission backs up the all-wheel drive.



Serious stoppers
Further expanding the RS 4's performance repertoire are massive 14.4-inch front rotors with fixed eight-piston calipers. The system's strength is in its ability to invisibly turn massive speed into heat without drama. It will, without a reduction in performance, slow the car from 130 to 70 mph time after time. NACA brake ducts in the underbody reduce brake rotor temperatures by 170 degrees at speed.

Under heavy braking we found the RS 4 slightly nervous, which was disconcerting at high speeds. This behavior is likely the only perceptible result of the undeniable effect of physics, given the RS 4's engine position. Its front tires bear 59 percent of its weight in static conditions. Increase that burden with some massive weight transfer, add in the effects of aerodynamic forces and driver reaction and squirminess is the result. It's not a deal breaker, but it will wake you up if you must slow down quickly.

The massive brakes conspire with the RS 4's sticky Michelins to haul the car from 60 to zero in only 107 feet and exhibited zero fade during our testing. In fact, as their temperature rose on consecutive runs, braking distances decreased — the mark of the truly high-performance system. Pedal feel isn't as solid as we would like, but it is as stubbornly consistent as any racecar we've driven.

Tall order
Stephan Reil, director of technical development at quattro GmbH (Audi's performance tuning division), is the man largely responsible for the RS 4's driving character. He told us Audi benchmarked cars like the M3 CSL and Porsche 911 Carrera 4S when developing the RS 4.

He wouldn't tell us which one was fastest around the Nürburgring — a little matter of political correctness he claimed — but he did say that the RS 4 was capable of lapping the famous circuit in the very low 8-minute range.

Reil's biggest goal was that RS 4 drivers be able to feel the character of the car, which is the real reason the stability control can be fully disabled by holding the ESP button down for 3 seconds. Push it once and it simply disables traction control. Hold it down and you assume full responsibility for the RS 4's dynamics. We like full responsibility in a car this capable.

The look, the feel
Adding some sex to all that stomp are the most bulging, glorious fender flares this side of a Renault R5 Turbo. They're necessary to cover a track width 1.5 inches wider up front and 1.9 inches wider in the rear than the S4. Given the rear fender change, Audi's stylists saw fit to carve in the most brilliantly integrated rear deck lid spoiler ever devised. It adds a touch of functional class to the car's hindquarters, and in combination with the flares, makes the RS 4 look like it can deliver the business its engine promises.

The split seven-spoke wheels measure 19-by-9 inches and do an appropriate job filling the fenders with 255/35-19 Michelin Pilot Sport tires. The RS 4 sits 1.1 inches lower than a standard A4 as well.

There's no confusing the RS 4's interior with that of the standard A4. Silk napa leather lines all the seating surfaces, and the heavily bolstered front seats are embossed with the RS 4 logo. Carbon-fiber trim accents the dashboard, door panels, center console and ashtray doors front and rear.

Serious go
At the track the RS 4 proves its mettle, launching from zero to 60 in just 4.7 brain-cell-punishing seconds. The quarter-mile disappears in 13.2 seconds at 106.8 mph.

The shifter and clutch take-up don't have the near perfect feel achieved by the BMW 3 Series or the quick-action of the Mitsubishi Lancer Evolution's controls, but they aren't cause for complaint either. Luckily, with such a spectacularly flexible power plant, you don't have to use them as often as you would in either of those cars.

Through the slalom the RS 4 again defied conventional thinking by demonstrating an almost unthinkable ability to go where it was pointed. Its 70.6-mph slalom speed ranks it second fastest among every sedan we've ever tested. Mitsubishi's iconic Evo holds the record only 0.1 mph faster at 70.7 mph. Lateral grip was also stellar at 0.90g, with at-the-limit balance tending toward mild understeer with reasonable adjustability.

You get what you pay for
All that performance doesn't come cheap. Our test car, which was fully loaded with the $4,700 premium package and rear side airbags ($350), stickered for $73,870 including destination fees and the mandatory $2,100 gas-guzzler tax.

There's no denying $70 grand is a lot of green for any car, even one this capable. But there's little doubt that the RS 4's biggest competition, the upcoming BMW M3, will cost about the same and make similar power. It might not be cheap, but it's hard to put a price tag on soul.