If you're gonna track the car, Evo all the way. S4 is too heavy (even with awd). Minimal money into the Evo will make it fly around a track.

 

Don't know much about B5 S4, but I had a B6 S4 (340 hp V8, 6MT, awd) that was great on the street, but a fat pig at the track. Just way too heavy in the corners. And the stock clutch was a piece of crap. You could destroy in one track day, and I'm not talking about abusing it -- driving the same as I would in my EVO and the stock clutch probably lasted 40 track days or more.

 

So I guess you have never seen the video of the fq-400 ( factory suspension and motor mods) passing the lambo on a road course?

 

Having owned both cars, an APR stage 3 S4 and now an 04 Evo, I can say that the Evo hands down wins in the "fun to drive" category on the track. My stock evo handled so much better and took a lot less work to drive than dumping $20K+ into my S4. The S4 made a much nicer daily driver and I miss having it, but taking the evo out on the track makes me not regret my decision at all.

Also, I would not buy the Buehn turbos. I have personally seen at least 3 sets fail locally. Though there are several of the RS6 wheels that have seemed to hold up fairly well. I personally would not run anything other than a straight K04 or go with one of the new GT kits that have been produced.

 

Just in my opinion right out of the box B5 S4 has nothing on EVO RS, except style and comfort. I currently own both cars.

Even Stage III S4 w/ brake and suspension mods will have trouble w/ stock EVO IX RS on the track. EVO is wicked fast right out of the box, add -2 camber and even stock Brembos and stock A046 Yokohamas are sufficient enough to keep up w/ modified S4.

At the same time search for NorCal/SoCal NASA TTA car driven by Patrick Lindsey.
It's a B5 S4, w/ full cage, penkse shocks, KO4 400HP engine riding on 245 Hoosiers. He sets faster lap times than some guys in TTU.

Actually in NASA Nationals he did:
TTA Patrick Lindsey 212 1:36.863 S.Cal 01 Audi S4
While fastest car was AMS EVO 8:
TTU Jon Krolewicz 70 1:34.366 S.E. 04 Mitsu EVO 8

Sure it's 2.5 second difference, but atleast 1 second can be explained by wider tires used in TTU, stock S4 fenders don't allow anything wider than 245, even RS4 fenders barely fit 275 rubbers.

I believe AMS EVO 8 car is using APR wide body kit and 18x10 wheels, probably using 295 race slicks. That alone almost explains 2.5 second difference.

Plus AMS EVO has built 2.3L block, while S4 is running 400HP Stock like RS4 power.

EVO RS is a much better bang per buck than Audi S4, yet I think B5 chassis has a lot of potential, at this point I think it is possible to build 97-2001 1.8T powered A4that can kick stock RS butt for the price of EVO IX RS. However, I decided not to bother w/ the headache and bought brand new EVO IX RS, which also comes w/ a nice warranty .