1971 was a different story indeed. Ford, Chrysler and Chevrolet all left the series, the only works team remaining was the Sunoco Penske AMC team. Of course, the top-line drivers left too. The reason behind all this was the decline of the Pony car market, combined with an over-competitive 1970 season.
The Under 2500 series had two separate races now, the other 8 still combined with the over-2500 series.
Not surprisingly, Penske won the manufacturers title, winning 7 races out of 10, while the Bud Moore team took the other 3. The Under-2500 was more interesting, Datsun taking the title only in the last race.