<font face=\"Verdana, Arial\" size=\"2\">...a 2 wheel drive (FWD) V6 Audi would have a chance???</font>
I would guess unlikely. Although similar in stock horsepower to the 325 (190hp Audi vs 189hp BMW) and somewhat similar stock weights (3087 v 3352), the Audi would be at a significant disadvantage with front-wheel-drive. Even if given a 200-pound weight break versus the BMW I think one would be hard-pressed to be able to keep the A4 from burning off the front tires in chase.
The AWD system in the Audi is basically a FWD system with three driveshafts tacked on. I think the F/R split is - at most - 60/40 F/R. I'm confident the A4 would need the AWD just for parity at similar race weights to the BMW. While not a direct comparison, one can review the Stasis AWD A4 to the Turner BMW RWD 325 in the World Challenge series and see there's a certain level of parity, with the A4 weighing quite a bit less.
Mid- to late-90's V6 A4s are coming on the market real cheap, and I think the A4's suspension design is excellent, possibly on par with the BMW's. Further, there exists reasonable amounts of aftermarket support for the car, but NO WHERE near the development and support for the 325; you will likely be doing most of your own development. It would be a fun project, though.
If one can get a 150-200 pound weight break over the 325 then I'd be game for building a FWD A4; however, at comparable weights I'd tilt my hat to the AWD version.
GregA, still thinking over the idea, and wouldn't it be fun to drive at Audi Club HPDE events...? Think anyone would notice if I stuck my S4 drivetrain in there...?