Correct me if I am wrong but the rear O2 sensors have no effect on the air/ fuel or anything else they are just there to confirm that the cats are working? The reason I am asking is I will be driving with open headers to the muffler shop then I will be driving with no rear o2's for a dyno tune.

 

The rear O2's are only for verifying that the cats are working. You may throw an SES light, but it will have no affect on performance during the dyno tune.