I have read all of the threads on these questions and unless I have missed something, I did not find the answers... I am wondering if installing a quality 4-2-1 header will in any way hurt fuel economy on the QG18DE? Other than the loss in fuel economy due to you driving it harder with the new found "power", with the cat's being removed will the O2 sensors throw the fuel trims out of wack and cause poor fuel economy? And will it set a CEL due to the cat's being removed? I am rather focused on this because my wife hates the CEL, and she commutes roughly 70 miles a day with it, so I don't want it to have a decrease, but alittle more power pulling onto the interstate would sure be nice! Any experienced input would be greatly appreciated.