I had originally planned on running an ORY pipe (I already have it actually) and have a set of O2 sims for that setup. I'm now planning on putting a set of cats on the y-pipe, should I still run the sims or have a set of bungs welded in and run actual O2 sensors behind the cats?

Since I'm taking AIR and EGR out of the equations, I'm thinking just sims.

Thanks,
Chris

 

You have 3 choices: Real O2 sensors will tell the PCM if the cats are not doing their job. O2 sims will tell the PCM the cats are always doing their job. Tuning out the rear O2s will eliminate any issues. Since you will need to tune out the EGR and the AIR messages, it would be easy to tune out the O2s at the same time.
Your call.