NHRA’s tech department determined the process needed limits.
In a memo issued to teams on July 12, NHRA's tech department said, "Effective immediately the minimum header angle will be 32 degrees. Additionally, there will be a maximum header pipe O.D. of 2.75 inches
as well as the I.D. must remain constant beginning 8 inches below the header flange to the exit of the header (i.e. stepdown headers not permitted).
"We will continue to evaluate header angles with possibly making additional rule changes for 2017. If additional rule changes are made, we will communicate these change(s) prior to the end of the 2016 season."More info