Race on Sunday, sell on Monday. It’s an old strategy in the car business, but one that seems to work. The one-model Jetta TDI Cup race series, designed to promote young, up-and-coming drivers in identically prepared race cars, has been Volkswagen’s entrée into the world of trackside marketing since the 2008 racing season. The unexpected twist for most spectators — the series piggybacks on the ALMS schedule — is that the race cars are lightly modified Jetta TDIs that are run on B5 biodiesel fuel. The racing is exciting and, importantly to VW's marketing efforts, it makes the case that diesel-powered cars can be exciting as well as economical.