Do I have to install the high speed pinion gear if I want to run the 2 traxxas nimh batteries in series for higher speed?
Just wondering if I will over heat the motor or esc with the stock pinion gear in it?
You should probably, but in the case you dont. Just watch your temps on both motor/esc and batteries
YES! If you don't you will fry your esc in a hurry. This forum is full of people who have. Even with the right gearing you are really only supposed to do occasional speed runs. The stock esc has issues with running two batteries in series so if you aren't still under warranty be very cautious.
Rally SV2/4600 and fully loaded