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 1978 Ford Mustang II, entries with the 302 cubic inch engine and a factory rating of 139 currently rated at 139 has been increased by sixteen horsepower, to 155 horsepower; for Stock Eliminator.

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 609, has been increased by twenty six horsepower, to 636 horsepower; for Super Stock Eliminator.

The horsepower rating for 2012 Ford Mustang Cobra Jet, entries with the 330 cubic inch engine and a factory rating of 510 currently rated at 588, has been increased by twenty horsepower, to 608 horsepower; for Super Stock Eliminator

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. 3, 2013.