ORIGINAL: cumquat
i had this same idea. i had the idea of using outrunners as they have a low profile and are supposed to produce more torque than any standard 540 or 550 size motor. from what i pieced together looking into building mine, something around 400kv should work. with a 2.5'' tire on 4s, it'd be going about 44mph and i imagine that 4 of them would have enough torque to get 3 or so pounds moving with little issue. only reason i havent built mine is because i dont have the money for the motors and ESCs i was looking at yet.
out-runners are my deal! very powerful, very efficient and run very cool. a 450/500 heli motor eats the same power as a hot 540 inrunner but has the footprint the size of a 380 inrunner and has a 3.17 540 sized shaft.
check hobbyking, my 4400KV was $12 and they have nearly any Kv and size availible.