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What is the gear ratio? I'm with Brett 4500 is very low, since you are getting 34mph I think your tach might be off.

(((RPM/gear ration) * pitch) * 60) /12) / 5280 = Theoretical Max MPH without slippage. Your current #'s show gear ration of 1.88:1. If this is not very close then your tach is wrong.

With a lightly loaded boat a SS prop of the same pitch is not very likely to make much of a difference in top speed.
 

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I looked up gear ratio it should be 1.85:1 and at 4500RPM that would be approx 34.5 mph, slippage accounts for the amount less than max theoretical that you measured. 4500 is the min WOT and 5500 is max WOT operating range for that motor.

To get higher rpms from prop change would mean less pitch. It is doubtful that you would get the 1K rpms to hit max WOT range from a 13P. I think you'd pickup little less than 500 rpm's from the 13P and you would lose couple mph's.

I do not think you are going to get more speed. Unless the motor is under performing or the boat is heavier than it should be. Sounds like 15P is the right pitch to get max speed out of that motor/boat combo.
 

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Your original post ask for a prop that was going to give you more RPM and speed.

As I previously posted I think there is something else at play other than prop, if the current prop is in good shape.

So if you want a SS prop just to have a SS prop A Michigan wheel ballistic would be a good choice. I doubt it will achieve your original goals.

You will hear all kinds of opinions on the question. Most often peoples reaction or opinion on a brand of props are very closely linked to the performance.
 

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Discussion Starter · #11 ·
ok guys i went today and bought some things for the boat fuel filter, oil, waterpump kit (not instaled). i cranked my motor up to run it for a while and notice im only running on two cylinders :mad: :mad: :mad: :mad: one of my coils are bad so i think thats whats causing my 4500 rpm problem !!!!
 

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If you get to 5500RPM you should be at 40MPH or so, accounting for slippage.

Glad to hear you found the real problem. So lets say you get 40mph by fixing the coil that is 6MPH better, it is cheaper than a prop and you should see way better fuel economy as well.
 
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