The ad climate for a start-up is obviously tough. American Thunder says it has a paid circulation of 185,000 and has hooked some NASCAR sponsors, including Viagra. But it still needs to attract an automaker, the traditional breadwinner for new publications. It also must compete with men’s lifestyle magazines like Men’s Journal and racing publications like NASCAR Illustrated. One breakthrough has been a deal with Wal-Mart to distribute American Thunder in more than half its 3,100 stores. “A lot of our shoppers are NASCAR fans,” says a company spokeswoman. “It makes perfect sense.” Gentlemen, start your cash registers.