Or you could upgrade to a 36 Volt 1000 Watt motor such as our MOT-361000B. This motor would provide a lot more power and torque that the currently installed motor has.
A power contactor such as our RLY-24150 or RLY-36150 could be substituted for a variable speed controller and it would provide unlimited current to pass from the battery pack to the motor as opposed to a speed controller which would limit the amount of current. However electric scooter motors are designed to be used with speed controllers and using them with a power contactor could possibly over stress the motor's shaft and sprocket and cause them to break or strip due to the instantaneous acceleration that a power contactor would provide.
As far as top speed goes any of our larger 500 through 1000 Watt motors would have the same or higher RPM than the currently installed motor has so the top speed would be the same or higher than it is now. The current motor may be lugging due to a higher than necessary gear ratio though so a more powerful motor may provide a faster top speed due to this. We have a top speed and gear ratio calculator that can be used to determine the top speed of the Power Wheels racer with any motor that is installed in it.
Using the right gear ratio for the job is one of the most important things when fast acceleration and hi torque are required. For instance if a motor was geared for a 20 MPH top speed then it would accelerate much slower than if it was geared for a 10 MPH top speed. We can help with running gear ratio and top speed calculations if you would like.
Please let us know if you have any questions.