It forces the torque converter to lockup even under wide open throttle. When you hit 3rd. gear you lock it and you will get a few more miles per hour in the quarter and a little faster trap speed. Right now with my automatic, if I am going wide open on the interstate, when I hit 135mph I will hit the rev limiter since it won't let the torque converter lockup under wide open throttle. I am mainly wanting to do it to get a little better quarter mile time and speed, but I also want to be able to force it to lockup if I am flooring it and nearing the rev limiter in a high speed run on the interstate.