Hello: So, I've been reading several of the topics on increasing the Drifter Fury power, speed and ride-time. My boy (10) races his buddies around the block (all are stock) and has expressed the need for a little more speed. What is the fastest, easiest, cheapest way to accomplish this? Believe stock speed is ~12mph. Getting >15mph is desired. Please help, seems like there are many options here. Looking for the quickest bang for the buck. Plug and play motor? Sprocket? Controller? Thx for any guidance you can provide!!