Audi's RS cars are highly focused driving machines, featuring specially tuned engines along with brakes, wheels, tires and suspension upgraded to suit. More overtly bulged wheel arches, front and rear spoilers, larger wheels and unique interior trim are other motifs that flaunt their purposeful mission.
Audi's S cars, on the other hand, are a more straightforward transplant of standard-tune V6 or V8 motors from the model range above, instantly improving the power-to-weight ratio. With little to identify them other than different wheels and subtle badging, these are genuine stealth machines which suit a certain type of customer.
London-based Dr. Theodore Soutzos is one such man, but the stock S4's 344 bhp was far from enough for him. Introduced to the highly respected British Audi/VW tuner AmD, he was told his Audi S4's V8 had plenty of potential headroom.
AmD always does a before and after dyno session, and Soutzos, like every car enthusiast, was keen to know just how much power and torque his standard 7,000-mile S4 had. Using the base dyno numbers, AmD estimated a peak of 338.6 bhp at 6383 rpm, about 5.5 hp down on the claimed 344. However, the 324.6 lb-ft of torque at 3259 rpm was substantially better than the rated 302 lb-ft at 3500 rpm.
AmD's Stage 3 conversion for the S4 centers on an ECU remap and a complete UK-made Milltek Sport stainless-steel exhaust, which replaces the stock system from the manifolds back, and includes new downpipes with free-flow 200 cell catalytic converters. Visibly larger rear exit pipes fill the factory cut-outs so perfectly their extra diameter is only apparent to the cognoscente.
Correcting for driveline losses, flywheel output is estimated at 395.2 bhp. AmD claims more than 400 bhp for its Stage 3 conversion and speculates Soutzos' car was a bit down on power to start with. But it will get better with use and should be making more than 400 bhp at 20,000 miles or so.
Apart from improved performance and tractability, the owner has also claimed an improvement in fuel economy, since in normal driving less throttle is required to achieve the same performance as before. That said, it is hard to drive normally in this car on the open road as the engine is now so much more responsive and revs more freely. The AmD-tuned S4 now feels totally balanced, which proves our point that the standard chassis is indeed faster than the engine.-Ian KuahAMD www.auto-amd.com