As the result of runs under the Automatic Horsepower Factoring System (AHFS) 1.20-second under policy at the Chevrolet Performance U.S. Nationals, the following changes have been made.

The horsepower rating for 2010 Ford Mustang Cobra Jet, entries with the 330 cubic inch engine and a factory rating of 500 currently rated at 636, has been decreased by twenty six horsepower, to 609 horsepower; for Super Stock Eliminator.

As a result of an error found in the race data, the horsepower rating for 2012 Ford Mustang Cobra Jet, entries with the 330 cubic inch engine and a factory rating of 510 recently rated at 608, has been decreased by twenty horsepower back to its previous rating of 588 horsepower; for Super Stock Eliminator.

The index for SS/AAA has been decreased by .2 tenths to 9.20.

NHRA's 2013 Automatic Horsepower Factoring System outlines that any run of 1.20-seconds or more under the index will receive an immediate index decrease or horsepower increase. These changes are effective Sep. 5, 2013.