I got an 05 xlt 5.4 and im running all four cats, with no muffler. Im about to get a new cat-back exhaust system, so could i cut out the rear cats, put some straight through pipe in place of them, then run the cat-back system?? And would cuttin the cats off make it any louder?

 

Yes it will be louder. Just make sure you do not have emissions, or a sniffer check, cause you will fail.

Before rear cat delete
http://www.youtube.com/watch?v=hA4b28XFLH4

After
http://www.youtube.com/watch?v=f4ptCHa5m4U

 

x2

i would hack all 4 off and do 2 hi flows