Re: Prop size for 4-107
I have the 4-108 on a Tayana 37, which is smaller than your Gulfstar but probably a bigger displacement. It came with the 17x11 3 blade, however from day one I switched over to the 17 inch max prop. The max prop has flat blades so the efficiency is not as great as the curved blades of a fixed prop so the pitch will be somewhat different. I played around with the pitch and when I matched the pitch to the original prop I was not happy with the performance. I wanted more speed at a lower rpm. For the last twenty plus years I've have the prop set at around the 14 inch pitch mark. The rpm of the 4-108 is rated at 3600 continous and I can not achieve that with the 14 inch pitch. I'm happy to cruise at hull speed doing 2500 rpm which is 80% of what my max achieveable rpm under that 14 inch pitch. Most people believe that you should be able to achieve the max rpm rating of your engine....which I can not.