whos right?

a few of my freinds and i were discussing dual exhausts, 2 of them said dual exhaust decreases fuel economy, my other freind argues that dual exhaust is better on gas. Whos right and why?

really depends on the engine size, design, etc...

correctly done, it should optimize engine output, sound, MPG, etc. but sometimes, people pick one thing to go with and forget out the others...