Re: changing from 1:36 to 1.50 prop selection
to get a good place to start and assuming you're going to go with a mirage or something similar, put your previous gear ratio and rpm into a prop slip calculator and calculate the theoretical speed. (BAM has an easy one to get to on the web). Now change the gear ratio to your new one, leave the rpms the same and change pitch until you get the same speed again, but with the new gear ratio. This will get you in the right balpark. Note that all other things equal, prop pitches in the pitch = 2x diameter, or 28-30 pitch will generally give best top end over 60 mph, but are hard on hole shot.
When I put your two gear ratios in I get that you need to go to a 25 pitch prop to get about the same top end. Not sure if you're running a mirage or a mirage plus... Mirage plus is what's available and can be had new up to 29" ....
Hope this is helpful...
