Just having headers bolted to the heads causes backpressure, not much but some. Back pressure is not totally needed for a good exhaust. And most vehicle, the less you have(up to a point) the better it will work. especially on forced induction engines. Less back pressure means better airflow through the motor making the SC more efficient. If you have straight pipes from the headers back, no muffler and no cats, there will be plenty of backpressure for your engine. And back pressure is not needed for a/f readings. As long as your O2 sensors are functioning properly, the only thing requires is exhasut gasses to be flowing by the O2 sensors for them to read correctly. As far as the reason exhasut tubes are bent twisted the way they are, it's usually for routing reasons, not to create backpressure. Get rid of the cats, and you will be happy. As you said, if you don't know the reason or function behind the catalytic converters, you shouldnt' be screwing with your exhaust. If you have read anything about performance vehicles, you will know most run better without cats installed for less back pressure.