HK 4020 Series 4020-910 4020-1100 4020-1390 Kv (rpm/V) 910 1100 1390 Max Power (W) 1820W 1640W 1890W Max Amp (15sec) 65A 78A 90A Max Efficiency 85% 85% 85% Io (No load A) 1.95A 2.45A 3.45A Rm (Resistance) 0.015Ohm 0.01Ohm 0.007Ohm Shaft Diameter 5mm 5mm 5mm Gearbox N/A N/A N/A Motor Diameter 48.9mm 48.9mm 48.9mm Motor Length 46.5mm 46.5mm 46.5mm Motor Weight 285g 285g 285g Built in Fan Yes Yes Yes Max Rpm 30,000 30,000 30,000 Poles 8 8 8 Case Outrunner Outrunner Outrunner ESC Timing 20-25 deg 20-25 deg 20-25 deg ESC Switching Freq. 8-16KHz 8-16KHz 8-16KHz