the 4146x is smaller so it has a higher stall rate, you may find the 4146 makes the car always want to go foreward, even if you set the idle lower, i found this with the mip springs for the tmaxx, i tried these on the redcats since they were cheap, like $4 for 2 springs but the car always wanted to move, with the 4146x, its got a good stall rate, so the rpms have to be a little higher before the clutch engages. but i would do like rclynx says, get the one from the lhs so you can play then order the 4146x for a backup