Performance wise a single 3.5" exhaust flows just about the same as dual 2.5" exhaust, except it should weigh less given the same tubing wall thickness. It would just look funny with the stock rear valance. Whereas any other rear valance is just ugly, regardless of the number of exhaust cutouts. It's middle school math as far as flow goes. Also, a single exhaust promotes superior cylinder gas scavenging to an h-pipe or an x-pipe. Most people just prefer the look of dual exhaust. Also, a duel 2.5" is much quieter than a 3.5" single, because the lower diameter piping lets less sound escape, and there are usually two mufflers associated with dual exhaust and usually just one with single. That reason enough?
