Check this chart out for help. It makes it easy!!
If you want to run 4S, a 2100 KV motor will approximately give you the equivalent of a nitro engines' RPM range.
This is the appropriate speed for driving on an RC track.
Losi 8 Buggy + Truggy & Associated SC8
Tekno RC Conversion Kits on all
MMM, MGM, Xcelorin ESC's
Tekno Neu "square can" brushless motors
Polyquest - Neu - Flight Power LiPo's