running without cats..
 

what codes will i get if i run my a6 2.7t with no cats? will it effect driveabillty or just give me a check engine light?

if you run without the front o2 sensors the ecu will default to backup tables which are rich and it will run rough. If you run without rear cats it will through a CEL, but wont effect performance as they only deal with emissions.

im leavin the front o2 sensors in, just gutting the pre cats. i guess its called piggies?

If you want to run piggies properly you need to relocate the front sensors behind the main cats. There is lots of information on this if you search.

ive searched quite a bit, and found a thread on making piggies, i didnt see anything on relocating the front o2 sensors. From what ive seen most people are using spark plug defowlers on the main o2 sensors. whats the purpose of relocating the front o2s??

then you aren't looking in the right places. You can run defoulers and it seems some people dog get any codes but proper piggies have relocated 02 sensors. You relocate them so they get proper readings of post cat concentration

i see. Do you know the best place to relocate them too?

somewhere right behind the main cats. You should be able to find a picture of the right spot if you search.