What would be the loudest thing i could put on a 2005 XLT 5.4L, and still have back pressure and some performance? I'm not looking for "Great" performace, but i don't wanna lose any.

 

Loudest thing you could do is LT headers, 2.5" true duals with no cats, or mufflers.

Loudest muffler you could swap to would probably be the Flowmaster 10 series, or Dynomax Bullet. Better performance with the Bullet.

Loudest cat you could swap to would be the 94106 9" body from Magnaflow.