Is it better to put the wideband right after the flexpipe or after a test pipe? I already have a bung right before the resonator. Also, I am running gutted stock headers/ypipe with a 3" exhaust, will that play a factor going from stock y to 3" in placement/readings?

 

Ideally you want it within 12" of the final merge collector, but having it a little further away isn't really going to affect the readings all that much.