the wire is a temperature switch that goes to the light on the dash to tell you if the cat is hot . if u cut it the light stays on . cut it real short and earth it to something . problem solved .
i read a book once about doing everything to a mr2 including v6 conversion and twin charging and turbo only and so on and replacing the cat with a straight pipe gave 40 more horse power . . they were already up around the 4-500 hp mark tho