Well if it still flies pretty light on its wings with the TT46 on it your only real option would be to step up to the next size engine. That would put you in the 60-90 size class. That class is kind of odd since most 60 size 2-strokes weight the same as 90 size 2-strokes. If you have the ability and room to move your battery back far enought to compesate for the added weight of the bigger motor go for it. DO NOT think that some other "40" size engine will bring your plane to life because it WON'T. The TT.46 gets great reviews and isn't the strongest thing out there but is a real decent engine in the forty class and has a real large happy following.

If the plane sucks now putting a bigger engine in it is either going to make it a lot of fun to fly, if the wing loading isn't to bad or make it snap happy. If you fly the plane rather fast then you will probably love a larger engine. Your landing speed will go up of course but so will your veretical performance. A great engine to look at in the 60-90 class is the OS .90 2 stroke. It has, just like the TT, a great following.