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Prop specs for 1976 70hp Johnson

Hello Bronson,

I have attached a list of the props that were manufactured for the model only below also please refer to the home site for purchasing help support this free site.. Props
you also can take any of the OEM prop number to the top of this page and past it in the part number search it will then provide prices and availably of the OEM and all after-market props that we carry that are identical.

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Haffiman37 thanks for your speedy response I am very novice when it comes to marine so apologies for the vagueness. I am not sure what the sizes relate to. I do know that there are 3 cylinders and that the exhaust runs through the prop. I am not sure though what size the prop is do you measure from tip to tip? or rather tip to hub. Also, what is 1/4,3/4 is that the prop shaft diameter?
 
For a prop marked 13 3/4 x 17, the first, 13 3/4, indicates diameter of prop (tip to center x 2), the second is Pitch = prop moves 17" forward in one turn.
In your case, the easiest might be if you know the about speed of your boat at max throttle.
15" pitch, give 20+ knots, 17" pitch gives normally about 25 knots and is the most commonly used.
Use a tach and check your max rpm, it should be about 5500.
 
A 13 1/4 X 17 prop is pretty standard for the 70HP engines. I had a '78 Johnson 70HP on a fiberglass tri-hull that did okay with the 13 1/4 X 17 ( about 5000 RPM), but did much better with a 13 3/4 X 15. The decrease in pitch helped the engine get a few hundred more RPM on the top end and made it rev quicker on the bottom end.

KJ
 
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