The Minnesota Historical Society has put some of its photo collection online. If you follow the link its search page and try some of the usual keyword combinations (automobile racing, racing car. etc.), you can come up with some good pictures. Most are from the Minnesota State Fairground. Some are from the early 1900s. The majority are pre-WWII. A word of warning: the dates on a lot of them are wrong, as are some of the captions. They're still pretty interesting, though.