I know zinger props say that to switch to a 4 blade prop you need to go down in pitch and go down in blade size. Right now I have a 16 x 6 on my OS 120 4cycle, so this means I need to go down to a 15x4 or like w8ve said try the 14.5 x 11. Going by zinger website I think the 14.5 x 11 may be too much pitch. Anybody else have any suggestions. Again it is going on a World Models P-47 thunderbolt.