The power advantage enjoyed by the BL4 15 Series motors is due to carefully shaped silicate-iron stators - which maximize wound copper and minimize magnetic shorting between the plates - plus extremely powerful, optimally-shaped magnets on the rotor.  Kevlar sleeve on the rotor allows the BL4 16 series to turn up to 40,000 rpm continuously. The internal resistance of the motors is identical to other 6-pole motors in the same class, but the Kv is much lower due to the stronger magnets.  That's why the Warp 4 motor can turn a larger (or higher pitch) prop than the competition at the same amperage and voltage. Motor Type #Cells No Load  Amps  m W Kv Short Time Max Amps Weight ACn 16-15-3 6-14 1.70 27 3000 30 76g Max A Continuous Max W 5 minutes  Max A 20 sec 26A 260W 40A