The Y harness runs the packs in paralel, you will double the current (Amps) and not the voltage, as the voltage stays the same, but you will need to make sure that the ESC will be able to handle it as the current will increase, if you have 2 7.2V 3300mAh packs, that will then make it like one 7.2V 6600mAh pack.

Anyway, I am running a starterbox that requires 2x motors, I am looking for 2x modified motors, but I dont need speed, I need torque. please put me in the ballpark as to what I should look for, I am a nitro guy, and not electric.