I wouldn't advise using 4s with the stock motor.I know others have tried some worked a few runs but all have gone up in smoke or melted fan housing and burned the motor. A successful 4s set up is jet screamer motor with a 3 or 5 blade alfa fan or the sf fan supplied with this kit. The jet screamer is a direct fit into the sf fan available at hobby lobby. Using the alfa fan with the five blades expect this f-16 to go well over 100mph and unlimited vertical[X(] also need a 20 to 30c lipo able to handle about 30amps draw 2000mah to 2200mah should work fine. Oh one other thing close off the cheater holes on the sides of the plane. It will sound more like a turbine(real jet)......Tim