the os .46 la is a bushing engine that isnt ported very aggressivly (ports are the holes that allow fuel/air/exhaust to enter and leave the engine, the larger the ports the more powerful the engine...to a point)
now the ax.46 has ball bearings which help reduce friction and it has larger ports so its more powerful

thats about as simple as i can put it, i can get much more complex if you want an indepth explination