In February 1982, Buick announced a two-tone Regal named after NASCAR’s top series. It had a 125-horsepower V6, and only about 16 of the 215 built had a turbocharger. Five years later, the same name stood on an all-black coupe that could outrun a Corvette, and its final version, the GNX, ran 0 to 60 mph in 4.7 seconds. Few American cars changed character that completely in such a short time. A V6 Nobody Wanted…