From humble beginnings it has become the biggest prize in sprint car racing as the Knoxville Nationals open tonight with the first of two nights of qualifying. Forty-one years ago, 59-drivers entered the Nationals and Roy Robbins was the eventual winner. The event was the brainchild of then promoter Marion Robinson.Promoter Ralph Capitani who has seen the facility grow from wooden bleachers on the front stretch to a stadium that seats some 25-thousand fans. He says the original five thousand dollar purse was thought to be “crazy.” Now the purse is 705-thousand dollars and interest continues to grow.Capitani says as the event has grown it has become a big part of the city of Knoxville itself. Carol Geil is special events coordinator for the Knoxville Chamber of Commerce and says with 30-thousand fans converging on the town it is a boon for business.Geil says each year residents open up their homes to race fans since they only have two hotels in the area.The event sells tickets to fans from every state and also has an international flavor.Mark Kinser will try to become just the second driver to win three straight titles this week.