There is no such thing as 'a NASCAR.' NASCAR is a sanctioning body, not a physical vehicle. The cars that are raced in the top tier of NASCAR (Winston, er... I mean Nextel Cup) are called 'Stock Cars' or 'Stockers.' BTW, Stock Cars are not the only type of cars which are run by NASCAR. They also run Modifieds, and IIRC they run a dirt latemodel series and an asphalt latemodel series. Their subsidiary (IAC or something?) runs the Grand American Rolex Series and the Grand Am Cup.
Just thought I'd point that out...