Hey guys. I have a 2005 F-150 5.4L 4wd. I currently have "true duals" with a dual inlet/outlet Magnaflow muffler. I noticed a DRAMATIC decrease in low end torque when I had this installed. To resolve this problem, I am completely redoing my exhaust. I ordered a pair of PaceSetter long tube headers with the matching offroad Y pipe, and also the "lightning style" exhaust from Magnaflow (single inlet/dual outlet).

Now here's my concern. The Y pipe is "offroad" and doesn't have cats on it. I would like to have cats on, not only for legal issues, but to help my exhaust. I know that eliminating backpressure is bad (my engine is normally aspirated). I'm not sure if my original cats will fit on the Y pipe, being that they are 16" long. What is the REAL difference between stock and Hi Flow cats? Will installing Hi Flow cats (around 11" inches - easier to weld onto Y pipe) decrease my backpressure and put me right back at where I am now (loss of low end torque)?

If it helps, I have a AFE Stage II Cold Air Induction and an Edge Evolution Tuner. I want my low end power back! PLEASE HELP!

Also, has anyone installed headers on a 05 F-150? Do you have to raise the motor or trans?

 

what size pipe did you use? i used 2.25" and my system really enhanced my low end-phil

 

The "true duals" are ran with 2.5'' pipes from the cats back.

 

you lost your velocity on your lower rpms - you picked up some hp at 4k and above but these trucks need tq as they are so heavy -i went 2.25 " with x as close to original y as possible into 2 magnaflow mufflers my van is 8k lbs and i tow 6k lbs every weekend- trust me if my exhaust didn't help my low end- my 3" oem woiuld be back on in a heartbeat-phil

 

SIDO instead of duals.....Less $$$ and great performance!

 

I plan on doing SIDO soon on my 05.