mine has a spool and it gets more street time then 1/4 mile time. it is for sure not a good idea. mine only has one because i bought it that way, and it is a donar car for my project so i will keep it for now. but if you have a posi now do not change it. my car broke down once and i could not push it off the road into a parking lot, as soon as you deviate from a straight line the rear wheels lock up from one wanting to turn faster then the other.