Going for a lap of luxury
by Jay Chen
photography by Eric Kieu
We've always wondered how top tuned Euros would do at the Ultimate Street Car Challenge. And those tuners have been wondering the same thing. While we haven't had too many of these heavy, high-dollar hitters enter, there's no denying the performance potential of BMWs, Audis and Porsches. Now that decade-old M3s, S4s and even Carreras are becoming affordable, the USCC field is changing.
With typical German meticulousness, the people at Torque Factory in Venice, California, have been studying our contest carefully, reading all the rules, and measuring their performance against previous contenders and USCC winners. Such plotting and scheming has brought about specific procedures to evaluate how its 2001 Audi S4 (owned by Brent Mattraw) might do in our track, drag strip, dyno and emissions tests. The guys at Torque Factory think this twin-turbo S4 could be the dark horse that blows our rice burners out of the water.
According to Jeff Moss (big kse at Torque Factory), the equation for winning is simple: take the luxury and build quality of a top German performance sedan, then bolster the suspension, brakes and driveline. Leave in all the street amenities and power it with two massive turbos, stuffed into what little space there is between the block and frame rails.
As the Germans are known for over-engineering, Torque Factory, felt no need for additional seam welding, oil and diff coolers, or reconstructing suspension bits. This car was designed from the beginning to dominate the autobahn under sustained triple-digit speeds without breaking a sweat. We hope the same principles still apply now that the turbos are claimed to be pushing almost 500 wheel-hp.
Mattraw and Torque Factory also took some similarly simplistic steps to make sure their bottom end doesn't wind up on the dyno floor. Keeping the same bore and stroke dimensions as stock, the rods were replaced with Pauter E4340 vacuum melt forged chromoly rods with stock factory bearings. The original pistons and rings were stuffed back into the holes since, they claim, much of the factory cross-pattern honing marks were still on the cylinder walls. Stock head gaskets were replaced with 034 Tuning equivalents.
External engine modifications include a set of Audi RS6 turbos with RS4 compressor housings, in order to mate up to the S4 intake plumbing. With this much air, we're not sure if the two side-mount intercoolers will be sufficient to keep heat soak at bay at low speeds. The fuel system was bumped up a notch with 660cc/min injectors and an AWE/GIAC modified fuel system kit. Hopefully, it'll manage to feed those thirsty injectors under high-g cornering. GIAC tuning also provided several switchable ready-to-go fuel maps for the stock Motronic ECU to make big power on the dyno, traction-optimized boost for the track, and super-lean operation for our fuel economy drive.
To eliminate any push inherent in the nose-heavy Audi, the center differential was reworked to provide up to 80 percent of the power to the rear axle, held through a Sachs Racing clutch. This is then split by a tightly packed clutch-type rear diff. Taking the handling experience of Stasis Engineering, which runs three A4 World Challenge cars, the S4 was upgraded with Stasis-tuned Ohlin coilovers on all four corners, a Stasis rear anti-roll bar and adjustable front upper control arms. The car sits on 275-width Toyo R888 stickies all around, but with this much weight, it remains to be seen if this much rubber is adequate.
While the S4 will undoubtedly be the most civil of our USCC crop and lull the Girlfriend into a defenseless state of comfort, we still wonder if the near-stock old man styling, big power and a select number of race car bolt-ons will be enough to turn this Teutonic turbo sedan into a USCC winner.