2003 Audi A4 in Burbank

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.... Read full article