With the UltraFlos delivering the goods, we teamed them up with the X-pipe. The X-sound has a more pleasing pitch to the ears at 97 decibels (3 less than the H-pipe). A noticeably smoother idle and improved throttle response also resulted from the X-pipe. At three degrees higher air temperature resulting in longer engine heat sink, the X-pipe still managed to produce the best 60-foot time. Ironically, 1,320-foot e.t. was the same, probably from the extra heat.