I'm no automotive engineer I'm in the medical field but don't you need some back pressure or else you loose some of your low end torque? If I'm wrong please correct me, I'm trying to learn. This is a great site for learning.
1999 Harvest Gold F-150 4x2 SuperCab XLT Styleside, 4.6, Auto, Air box Mods, Tow Pkg, Alarm, Snug-Top Hard Tonneau cover(painted to match), 6-disk Pioneer CD changer, Kenwood Tri-Band Ham radio (2m,440,220), Billet grille, Bug Deflector, Clear corner lights, tinted front windows.
Planned Mods: Cat back exhaust, Headers, Superchip, 2/3 inch lower.