How do Headers (with the O2 sensor mounts) that move the Cat down below affect fuel econ? Or do they just remove the Cat all together? I've tried to figure out how it all works, but just can't wrap my head around it.

BTY.. Anyone who has a good exhaust setup... let me know! My HX exhaust (at least the muffler) is so skinny it looks like my poor car is exhaling through a garden hose

 

Most just remove the cat all together. Greddy, DC Sports, Skunk2, Megan, all good names in exhaust but you'll have to get EX header and exhaust bc no one makes an exhaust for a HX.(I think)