I had a cox Hyper Viper and it hardly had enough power to get off the ground--So i got bored and tore off the plastic fuse and i kept the styrofoam wing. I built a profile fuse out of balsa and made a nice beefy motor mount, i also cut off the plastic tail feathers and found a way to mount that on and work. I painted everything one color and I took out the fuel tank and i got a Cox .049 black widow. All in all it took about 4 hours but when i flew it, it was a whole new plane-- All i can say is wow

Thats just what i did.
If you dont want to go through all that work then go ahead and buy a bigger motor just make sure you put washers on one side of the motor to angle it out. This plane has a tendancy to let the lines go slack.