ok i dont know that much about exhaust but im learning haha so i would really appricate it if you guys can help me out... I have a 2004 f150 FX4 with true duals and X pipe no muffler and exit out the sides 45'd.. but i want it louder.. now my friend has a 2007 and just had exhaust done at the same place with the same set up he also got true duals x pipe no muffler 45'd and his is like night and day compared to mine lol.. now after doin some research he has 2 cats and mine has 4 cats.. and im readin alot of people cut the rear cats off or replace all 4 with 2 magnaflow highflows. i also have a S&B intake and gryphon with custom tunes. will i have any problems cutting the rear cats off.. or just cutting all 4 cats off and replacing them with just 2 highflows. like would i need to get different tunes for that set up or no. and this might sound like a dumb question but if i cut the rear cats off or put 2 highflows on instead will my truck run lean or anything. bottom line is, what is the better route without having any trouble with codes or my chip screwing up lol or would i be just fine cutting the rear cats off or replacing all 4 with 2 highflow cats

 

If you cut all 4 cats off and replace with 2 high flow cats you will need new tunes because you will run lean at that point. Same goes for if you just cut off the 2 rear cats you will need custom tunes because it will run lean. If i were you i would cut all 4 off and put the 2 high flow cats on and get the custom tunes. Hope that helps

 

You can do either or.