Stuffing a small car's engine bay with V-8 power is a strategy that dates to the era when cars had cranks. But Audi, preferring to lead instead of follow, wasn't about to traipse down that path without investigating alternatives. Two decades ago, the original Quattro kicked gravel in rally competitors' faces with five cylinders and 500 turbo-whipped horses. Successors to that beast earned their S badges with engine innovations du jour. Then, four years ago, Audi stepped up on the performance ladder with the move from five to six cylinders. Now, it's skipping a rung by loading its largest V-8 engine under the hood of the smallest four-door it sells in the United States.
It's fitting that the 2004 edition of the S4 sedan and wagon, arriving this fall, are discreetly attired, because Audi engineers were especially clever in the way they slipped extra power under the covers. Instead of muddling the S4's fine aesthetics, they pared two full inches from the engine's length to fit a 40-valve, 4.2-liter V-8 peg into a V-6 hole. Drive systems for both the camshafts and the external accessories were moved from the front to the rear of the block. Switching from toothed rubber belts to chains for the DOHC heads saved additional length. These alterations may sound straightforward, but, in fact, every major engine casting was changed. While the Audi engineers were busting their budget, they factored in the latest performance tweaks: lighter pistons and connecting rods, variable intake valve timing, and a dual-mode intake manifold.
The net result is major gains in both power and torque over the outgoing 2.7-liter twin-turbo V-6 engine with no appreciable increase in weight. Output curves are inflated to 302 pound-feet of torque at a handy 3500 rpm and 339 horsepower at a honking 7000 rpm. Obviously proud of what they had wrought, Audi's team of engineers signed off with an underhood presentation worthy of the Louvre: beautifully finished intake manifold and cylinder-head cover castings and brushed stainless fuel-injector rails set off by colorful ignition-wire and fluid-cap accents. The layout is a study in symmetry, with few molded-plastic bits to spoil the show.
The new engine asserts itself at idle with the slightly jittery tingle of a sprinter at the blocks. Leg the drive-by-wire throttle, and a healthy torque surge slingshots Audi's 3800-pound missile into motion. Beyond 1500 rpm, there's no longing for the turbo days. Through the midrange, the V-8 is smooth, quiet, and quick in its work. But revving it past 3500 rpm uncages the wild animal. Now the engine's growl is determined, as if a juicy beefsteak were hanging as bait at the seven-grand redline. Factory figures claim a mere 5.6 seconds for the sprint to 62 mph, which is more than a second quicker than A4s powered by the 3.0-liter V-6.
A wide-ratio six-speed manual transmission passes the punch to a center differential equipped with Audi's usual Torsen limited-slip device. As long as all four wheels maintain grip, two-thirds of the torque is routed to the front wheels. A few months after introduction, a six-speed Tiptronic manu-matic option with steering-wheel-mounted paddle shifters will join the party. Only the stick was ready for preview driving along Italy's Adriatic coast, a situation that drew no gripes from us.
Gear ratios are widely spaced in the interests of cruising comfort and fuel efficiency. The shifter moves effortlessly through its pattern, but attempts to insulate the knob from the commotion inside the gearbox were, if anything, too effective; it's slightly numb to the touch. Elasticity is also lost somewhere between the electronic throttle control and the dual-mass flywheel. The S4 responds eagerly enough, but a portion of its vitality has been sacrificed to the gods of refinement. A similar complaint applies to the steering. The effort is perfect for every occasion, linearity is flawless, and center slack is nonexistent. Unfortunately, too little road feel makes the trip from the front tires' contact patches to the driver's fingertips. Some sensitivity is inevitably lost when the front tires are burdened with the dual responsibilities of steering and driving.
The kit of sporting upgrades Audi added to promote the already superb A4 to a $45,000 performance prince is comprehensive. Ride height is lowered nearly an inch, and spring rates, anti-roll-bar stiffness, and damper calibrations move smartly in the sporting direction. Eight-by-eighteen-inch cast aluminum wheels are shod with 235/40YR-18 Continental ContiSportContact 2 radials. The speed-dependent power steering is quicker, and the front brake rotors are larger in diameter. A new dual-rate brake booster reduces the amount of pedal travel necessary to make the four-wheel ventilated discs feel as if they've sunk long knives into soft pavement.