I've always had bad luck with the twin 550 motor setups. They would always eventually burn out which I guess everything would eventually wear out but I mean, it was almost like they never had the extra juice to turn the big-blocks. I now use the Ofna blue box with the chrome top that comes with the single 750 motor. The one that I brought required assembly. But it a real good box. I paid $65 US for it at the hobby shop.