on my 7mgte mk2 swap, I took out: the whole A/C set-up,hoses condensor compressor and all, carbon canister and every bit of pollution shit that there was, the cat of course, the cruise control unit, some little unit that has a small filter beneath the intake manifold that is deleteable, engine check light...I put a small piece of black tape in front of it. My car runs great, boost is smooth, a little rich I think but not too much, and pollutes nicely for all the treehuggers lol You can also remove the stock fan and put in an electric fan BUT the stock fan pushes way more air, that 10 blade GTE fan really puts it out. But like he was saying little sensors and small stuff like that leave them alone.