http://nhraracer.com/content/general...342&zoneid=132
The link above takes you to NHRARacer website where it shows the 5.4L 4.0L combination was on the books for 2010 and 2012 engine combos approved for the showdown class. It was then removed by Mike D. after a few weeks.
kdanner,
it's plain and simple any time the HP in stock eliminator got above 500 HP both of those combinations became legal. The 2013 Cobra Jet came from the factory with 500 HP. By the end of the year it was already above 525 HP. So both of those engine combinations were legal in 2013.
Jim D'Amore