Frank as you said its all subjective with true duals - no dyno data I've seen on this forum proves true duals are better (or even as good) as a well done catback + Y-pipe. XChang makes 175 or so, I think somebody may have hit 180 HP with true duals - I hit 179 with Y pipe and Bassani (all 3 cats in place) and DEMON hit 187 HP with 2 precats in place, custom Y and catback (but he has some other mods). This tells very little though - different cars, days, dynos not same as comparions on same car, same dyno. And even then variables like A/F tuning may confuse results. FWIW SHO shop has claimed that true duals have been compared with Y and catback and found no better. I personally think the difficult of H pipe placement on transverse engine makes true duals less effective than on longitudinal engine layouts. So, true duals MIGHT be better but it is unproven in the SVT application. But still I think a good option if only from a cost standpoint.
