i have a N/A Catless from the header back you just have to go on needswings and buy the o2 J-Bung. they will make the o2 sensors think there are cats on the car and you will not get a light it works by puting the o2 out of the direct exhaust stream so the o2 doesn't pick up all the fumes and reads clean on the ecu. i had mine for a while and no engine light. AND the talk about car will not know if its running lean or rich the secondary o2s after the cats are only for cat efficiency the two o2s before the cats read air fuel so that wouldn't be an issue

heres what you need
O2JBung.aspxStainless o2 J-Bung