I have a 04 5.4 with a bullet and an exhaust cut out. I want a louder, deeper, more rumbly tone. I've been reading around the forums and I've decided replacing my cats is the best idea. The only problem is that there's different ways in doing this. I've read about replacing all 4 cats with 2 hi flow cats, leaving the pre cats and deleting the rear cats, and vise versa... I've read many contradicting threads and pretty much all I want to know is,

Which cats should I keep? Which cats should I delete? And with which cats should I replace them with so that I get a good sound, pass emissions, and get no CEL?

 

I can't imagine how pissed your neighbors are going to be when you wake them up every night with what almost amounts to straight pipes. If you want a deeper/more rumble, you need a different muffler and some good exhaust tips (like 4x18 or larger). The only thing that removing the cats is going to do is make is louder, and possibly more raspy. If you do alter the exhaust, get the hi-flow cats to replace the 4 you have now.

 

Just have the last pair cut off. The pre-cats are more or less hi-flow cats.