This is one of the things Jay wanted me to post and point out.
All removable multi-piece exhaust collectors / stacks must be securely fastened with EITHER an NHRA-accepted header tether or a minimum ½” (half inch) stitch weld located on each primary tube to prevent loss of collector / stacks during competition. A current list of NHRA-accepted header tethers is available on NHRARacer.com Reference 2015 rule book General Regulations page 3 & 4 paragraph 1:3 Exhaust 3rd sentence for more detail.
Also, if you go with welding the collectors, pay particular attention to the welding process. In the tech seminar this year, they noted quite a few cases of welds that failed allowing the collectors to fall off.