The S4 had the 2.7tt motor here in 2000, 2001, and 2001.5 (kinda a 2002). After that, they're 4.2 v8 until the spanking new ones. The V8 is a great motor, and the b6 v8 s4s have less issues than the b5 2.7tt, but they're pretty much how they come. If you want to modify it at all, you had better go with a b5 out of the two, as they are fast for cheap, inexpensive to buy, and have great interiors and driving experience. They do have a lot of issues though, and you'll be fixing stuff a bit.