Something to consider with a bigger prop is the prop disc drag will go up considerably with a bigger prop/slower rpm. Consider a nosen p-51 with a q-100 and direct drive 24x12 prop versus a q-100 with a 2.5 to 1 belt system and a 32 to 36" 4 blade, which plane would win the race and which one would look like a real P-51. A Sachs concrete saw has a nice v belt pulley on the back and would be a good place to start for a drive system, engines are 5.8 cube also. anyone like to consider this? A 7.3 husky concrete saw with a pulley would provide even more oomph.