Here are a few ideas...
1. Start a forum for car owners to show off their rides.
2. Create a gallery where car owners can post/upload pics of their rides for others to see.
3. Do both 1 and 2 on the same site!
4. Do something like
http://www.girls-on-bikes.com
5. Develop a classifieds website to sell cars and parts.
Money maker? Doubtful. You could get some traffic going, get some emails from sign ups and start a community, then sell it on Ebay. That could make you a few hundred or more depending on traffic and popularity. It would work best just rotating banners for now.
Good luck!