could it be back pressure? :idea:LOL, this is absurd, a straight through muffler that loses 20HP:lol: everyone calls flowmasters 'chokemasters' and says "don't buy flowmasters, you'll lose ~5HP" because of the chambered design, but this straight through is supposed to be FAR less efficient than even those.
sounds to me like there is some unaccounted for variables in this comparison, or even just an anomaly.