I am flying a Mojo with std servos, std rcvr, 4 cell. I have flown it with an OS 46 and now an OS 50. Ihave a Burrito with the same setup and and currently a YS63. They all work fine for 3d with the YS obviously the most powerful. I recommend a .46 2stroke for your Mojo. I find a well tuned, smoothly operating engine with reliable transition makes 3d learning go well. A finicky , stumbling engine with gobs of power isn't so good.