Well to start of it's a pontoon boat with 27" Vee bottomed tubes. Power is a
mercruiser 5.7L 250 HP modified. Manifold was changed to a Mercruiser Injection manifold set up for a carb. 4 BL Edelbrock marine 600 CFM. FULL MSD ingition Distributor, 6M controller, rev limiter,knock sensor, timing control and 8.5mm wires. Timing at 28 deg. total. Spark plugs are NGK Iridium TR6IX Exhaust manifolds changed to Stainless Marine. Silent select installed 4" tubes out the back. Alpha 1 Gen II outdrive. Here is the situation. I have run 3 prop tests within minutes of each test with the same water conditions. Prop 1 Mirage Plus 23" pitch speed 49.83 4975 RPM 19% slip, prop 2 25" pitch Mirage Plus speed 50.14 4550 RPM slip 20% and prop 3 Bravo 1 26" pitch speed 50.23 RPM 4250 (to low) 11% slip. Any ideas about what I missed or should change I should be 55 MPH or close to it.

Thanks

The boat seemed to like the bravo prop. Try a 22 or 24". Also try the revolution. It's the same prop as the Bravo, but with a little less diameter for the lower power applications.

first you are over propping that motor, sec i thing 28 deg timing total seems a little low.

22 bravo is my choice your your app or a smaller dia 4 blade 24
that should put you close to 4800 and with a slip of 15-17% you should be around
54-56,