Sell the downpipe and buy headers...because they come with their own. If you don't want to get rid of the downpipe...which btw you NEED headers on a GenV car with a 3.4" since you don't have NEAR the supporting mods...you should be at stock or a 3.6" at the lowest...then you WILL NEED a PLOG (which I don't think ZZP even sells anymore) or buy PEM's from 3800Performance. Otherwise...your gonna nuke your motor to smithereens.