my daughters barbie four wheeler battery died. so i figured i can take an old dewalt battery and wire it in to work. Now it goes 3x faster and rides wheelies, she loves it now. Now we wait to see how long the motor will last. We also took duc tape and and wrapped around the back wheels to get better traction. Trust me, IT WORKS!
The motors in the black one are standard 12 volt motors, and will not be as fast as the ones in the Barbie fourwheeler (assuming the same voltage to each). The 12 volt ones would run about the same speed on 18 volts as the super 6's do on 12 volts.