the B5 S4 has a 2.7L V6 bi-turbo motor, making 250hp to the crank (also out of the A6), in europe they had a B5 RS4, it was the same block but with better turbos(K04's), internals, and fueling that made 380hp but they never released a B5 RS4 in the states, as everyone else has said, i think it is a 2000 S4 that was assembled in 99' because the next year model comes out the year before,( like 09' models will be coming out this year), the owner could have just bought the badging but ask him what work is done to it. Hopefully if he put the badging, he built the motor like the RS4 motor.... but if you are looking for a S4 mine is up for sale
Audi FTW!!!