just got around to checking the stock i.d. of a traxxas 3.3 pipe. the stock i.d. is .180 in. i bored one to .220 in. but dont drill all at once, drill in steps. i think it did improve power. but i would not go any bigger than.22- in. the wall gets to thin. EDIT: this was on an aluminum pipe. i dont know how it would work on a plastic pipe.