i have a 94 LS, i did remove the CAT for a resonator. i wasn't really going for gas mileage improvement but for more HP. since i already remove it, i was jsut wondering if it affected the gas mileage on my car. hard to tell but im gonna put the CAT back on because its too loud. 1 or 2 HP at the top end is not worth losing my hearing, plus i would get more bottom end torque with the CAT back on. If i had LSVTEC on the other hand, i would leave it off.