I put the 2.3 pulley and a Calmini Cat-back. I noticed crappy milage and black soot on tailpipe, indicative of running rich. I do enjoy the performance gains (I get 10PSI at 6500rpm), (seat of the pants dyno). I would like to hook mine up to a wideband O2 (and dyno) and am considering an HKS S-AFC to adjust the fuel mixture. There isn't any tuner shops in my area and a wideband sensor with readouts (and logging) are $700 and up, not including laptop. Any ideas? I'm sure with proper fuel mixture I'd get a little more performance and better mileage.