All of the Mamba Max escs that I have run 4S very well. Just watch the cogging. If it coggs to a point that it is a problem, back off of the gearing a bit. If you still have problems, then check all of your connections. I've had major problems with my Quarks (two of them now) and had to send my Compro in due to software issues. My MMs have been rock solid, save the two that I had to send in, because I fried them overgearing on 5S.