First get the builders recommendations You need to know: The HP at what RPMs very important The aperture to determine the largest wheel that will fit The shaft Diameter to determine max wheel size for load
What I'm aiming for right now is finding a 4bt bta which is rated at 250 hp @2800 rpm. I am leaning towards this motor because its seems to be more readily available on the used market verse say a yanmar.
My current set up was a 350 with a 1.9:1 and a 1-1/4" shaft spinning an 18" wheel (don't have the pitch on hand)
Now I have not done nor know how to do all the math but I'm hoping and I may be wrong that I can stick with my current shaft or with a better quality 1-1/4" shaft like aquamet if I go to a 1.5:1
Did like you said. Looks like if I go with the 4bta 250 hp with a 1.5:1 I can stay with a 1.25" shaft but would have to switch out my current one with an aqua met or something similar for more strength. Which would certainly be easier that going with a bigger diameter as I would have to pay someone to do so.
Thanks for the suggestion.