RE: AX Engines
AX's don't spin as fast for he same amount of "percieved" power as there FX cousins.
I used 46 FX's and going to the 46 AX , I increased my diameter to find that sweet spot of power.
On a quickie 500 I went from a 8.8x8.75 APC pylon(46FX) 15,000+ RPM's to 10x7 APC sport for my 46 AX 13,5000 + RPM's and it is faster than the FX.
so what's different? , it makes more power in a lower RPM range, less noise (since it spins slower) & more torque at a given RPM.
Internally all the parts are different, even the bearings !
Get out there & FLY