[joe_padavano]

The X-pipe helps by allowing each exhaust pulse to "see" both mufflers, so you've effectively cut the muffler backpressure in half. Since the pulse pressure is also split between the two mufflers, you also reduce the sound level. I will caution that ending the exhaust in front of the axle has some problems. First, you're increasing the chances of an exhaust leak getting into the passenger compartment. Second, even if you don't have a leak, the extra heat of the exhaust in the rear axle cavity can accelerate the aging of rubber tubing on the fuel and brake lines (been there, got the t-shirt). Finally, I found that the exhaust noise resonated in the rear axle cavity, making the droning sound even worse at freeway speeds.