"used to be"? When is that? There are lots of very interesting old stories about rule bending in Nascar. Actually, it apparently started from the very first official Nascar race [1].

If you want racing series about driving civilian cars fast, they do exist. Nascar just isn't one of them. The only one I really heard about is "Stock Miata" racing, but I'm sure there are other series using stock street cars, or at least having the exact same cars for all competitors.

[1] https://www.theglobeandmail.com/globe-drive/culture/commutin...