capitan morgan

I wonder if anyone knows what size prop I need to put on my scarab sprint. I'm changing out the 3.0 in favor of a 260hp 5.7. Im also changing the alpha one to a new alpha one with the 1.50 gear ratio.
I know a few of you have already made this swap and I am curious as to what prop size will work best and what top speed anyone might have been able get after making this swap? I am hoping to acheive the 70-80mph bracket.

therabster

I think you only going to make 65mph realistically. The V6 models only did around 55mph and you only have another 50 or 60hp.