The un-finned smooth 1509 is the largest motor you are going to be able to run in a Stampede/Rustler/Bandit/Slash. Anything longer and you are going to have a real problem with the wires exiting the can hitting the tires. Even at that your gear ratio is VERY limited. I would look into a Medusa 70mm length as thier wires exit form the size vs. the end.