The 4-2-1 or 6-2-1 ark r-spec header is a highly designed racing spec header. it’s designed to get the most out of high revving race tuned motors. it includes tig welded connections, de-burred & ported inlets/outlets, for better flow, larger piping and a cnc mandrel with bent primaries. the primaries exit into a special laser guided-designed merge equal collector which allows smooth exhaust flow, ideal for racing applications. has increased dyno proven horsepower and torque from mid-range to redline and comes semi-brushed with mirror polished.