That's why I went with the dynomax race bullet mufflers. Straight through design makes it flow great. According to their web page it only removes 4db from the overall sound but with no restrictions.

 

Jack,

Don't man to hijack here; but I'm going an identical rout with the same truck. From what year and vehicles did your ECU and garnes come from, is your's MAF?

 

90 f150 reman 5.0HO mustang motor stock computer with SD. I have the O2 sensor in the rh header collector. Runs just fine on SD but I will eventually go to MAF for tuning reasons. More torque then stock but the roller HO cam is way different from the stock flat tappet cam. The new motor it seems to make its power around 2500-4500 RPM compared to the lower rpm peak torque of the old motor.