I just got a 2004 f150 super cab stx with the 4.6l v8 and the guy cut off both cats and left it. I want to bypass them and just put an o2 sensor in pipe.. does anyone know what size exhaust pipe is right there? And if this will/ won't work. Any help is appreciated. Thanks!
Oh and maybe a possible diagram? Thanks!

 

Factory head pipes are usually 2.5" but the location you're talking about is factory bent and may require 3" for fit over the existing pipe. There are "Weld-O-Lets" made to weld over a hole in the pipe that fit the O2 sensor threads but you want to be careful not to go too far to the back of the truck on the pipe and have the wires too short. As with any modifications to exhaust and O2 sensors you could experience fuel mixture issues on the truck and need to have the PCM reset for the new equipment. I'm an old guy, lol, so I think stock is good. Good luck