wow, i see alot of BS with this subject
first of all, your factory pipes are crush bent, just because there is no ripples, does not mean its not crush bent
second of all, exhausts can help MPG, but it mostly depends on the car & how bad the stock exhaust is to begin with, & how you drive
i work at the only tri-state area mandrel bending exhaust shop, I know a few things about exhaust
www.mandrelbend.com is our website