i think you are missing my point, the 46 AX is just as happy turning a 8.75x9 as it is a 10x6, and gives more speed in most 40 sized sport airframes. the AX is a torquer engine, it'll turn big props just fine, but it'll also turn small props with allot of pitch just fine too as long as you're propping it to stay in the AXs power band (RPM range) as previously mentioned they do not respond well when you try to hop them up with a tuned pipe and smaller prop attempting to get speed from RPM but if you keep them propped to stay in their desired RPM range you can get some speed out of the torque ported engine none the less.

other engines like the OS SX versions or the YS/Jett/Rossi respond great to tuned pipes and smaller props turning a butt load more RPM, the AX does not so not all engines respond to propping the same.

kc