Let the Sunset Park pie wars begin. This Friday, a Papa John’s franchise will open on 5th Avenue between 58th and 59th streets, right next door to neighborhood fixture Johnny’s Pizza and within a few blocks of two other mom-and-pop pizza joints. The Times chronicled community backlash to the new business in an August article; as of then, 2,200 people had signed a petition that sought to stop the Papa John’s from opening. One of the Papa John’s opponents went so far as to say that the chain eatery had planted itself right in the face of everything that is Sunset Park. There goes the neighborhood? GMAP