If you are talking weapon, it varies depending on the type of weapon but generally you are look something with 2500W+ of power, eg -

NTM 50-60
Scorpion HK4025 or 4035
Turnigy HeliDrive SK3

Discs and drums don't need such big motors as they are fairly aerodynamic. But if you have a beater or bar then you need more power, generally speaking. Binky has a HK 4035-560, max output of 3500W, running on 10S. Conker runs a massive HK 5020 with a max output of 5350W, on 12S.

Note, I am having to put up the maximum power ratings as many companies advertise their motors based on that number rather than the continuous rating. Easiest option is to go with a known motor like the NTM 50-60.