Cars are classed to make them competitive. You won't find a Festiva racing against a 911, because it wouldn't be fair. I assume you're running at an SCCA event. My suggestion would be to get your hands on a rulebook, as they'll tell you what cars go in what classes. You can check out www.scca.org as well. I have 2 Miatas. One (my 95M) is stock, so it races in CS (C-Stock). However, my local region (Philly) has introduced a new group of classes this season, and they're designed for street tire use, so when I run the 95, I'll be in STX2. My 02 Miata has a turbo on it, so it runs in SM2 (Street Modified 2-seater). I boosted the car shortly after I bought it (new), but this past weekend was my first time autocrossing that one. It was... interesting The rulebook will tell you what you can do within each class, how they're decided, which cars go where, etc. Check one out.