I know this is probaly a dumb noobie question, but I looked for right ups about it before asking. I guess there is a couple of questions about it different websites advertise rear o2 simulators. Has anyone ran these with a "test pipe" where the cats are? I know they aren't supposed to make any difference in hp or tq, but an engine is an air pump and anything restricting it decreases it efficiency. Thanks for any insight or advice.