Yoav,

I'm not familiar with the specifications and running characteristics of the motor/ESC you have, however, if both are capable of handling the voltage of 4s, you will definitely see a relatively large increase in current (amps) and power (watts).

When you increase the voltage from 3s (maybe 10.5 volts under load) to 4s (assume 14 volts under load), that is roughly a 33% increase in volts, and you will see at least that much increase in the current - so from ~40 amps to ~53+ amps, and a similar increase in watts from ~420 watts to ~740 watts. Those numbers would be exceeding the amp/watt ratings you have given for the ESC and motor.

Regards,

Dave