I'm getting ready to add a cat-back exhaust system on my wife's 5.4 Expedition. I'm looking for a system that will product the most low RPM torque gains with very little increase in the exhaust sound inside the vehicle. I'm considering Magnaflows 15608 system which uses their 5x11 muffler and also Gibsons 619991 Swept Side system. I'd consider another SISO system or muffler if it met my needs. On my SuperCrew, I'm running a SIDO system, using CGS Motorsports 4x8 muffler. It sounds great but it's too loud for my wife. My friend is running the same setup on his SCrew but is using Magnaflows 4x8 muffler. It sounds as loud as my system. How well do the cat-back systems bolt on? Have there been complaints about the systems not being bent properly, causing them to rub along its path or any other complaints? Any useful feedback would be appreciated!

 

I put on a 3" Gibson Swept Side on my 5.4 SCrew and lost low end power. I'm considering replacing the Gibson muffler only to a Magnaflow and then pinch down the existing 3" Flowmaster Y-Pipe down to 2.75" thats on the inlet side of the muffler to gain back the low-end loss caused by the over-reduction of back pressure of the Gibson and added Y-Pipe.