Fastest porp for 1974 70 hp

[nashwinter123]

Hi,
What pitch would be fastest for a 1974 70 hp evinrude on a 17' deep V fishing boat. Boat is a fishing boat so its closed bow and doesnt have all sorts of stupid extra fiberglass storage or anything like that on it. Boats from the 80's. But ya what pitch would probably get me the fastest.

 

[eclark53520]

Re: Fastest porp for 1974 70 hp

No one is going to be able to answer this with a specific pitch.

It's going to be the longest pitch that will still allow your boat to get on plane and reach full operating RPM. Which means, you're hole shot may suffer...

You need a tachometer and a couple different props. Hit the lake and figure out which one gives you what you want.

 

[archcycle]

Re: Fastest porp for 1974 70 hp

Search around for a dedicated propeller shop in your area or a marina. Some will let you leave a deposit and try out a prop or 3. Every setup is different. Even if someone had the same boat as you and the same motor and both motors were in the same running condition then even changing which mounting height the motor was set at would change what was the best prop. You can google various calculations of prop setups but in the end you're going to need to test on the water.

 

[Silvertip]

Re: Fastest porp for 1974 70 hp

Yup - props are not one-size fits all and without test information with the prop you have now we don't have a clue. You need to make several wide open throttle runs with what you consider an average load and note engine rpm. If the engine cannot reach the upper end of the manufacturers recommended WOT rpm (about 5500 - 5800 in your case) then you need a prop with LESS pitch than you have now. If the engine tends to overrev, you need a prop with MORE pitch. Engine rpm changes about 200 rpm per inch of pitch. It increases with less pitch and decreases with more pitch. Speed will be whatever that prop delivers. Prop related questions should also be posted in the PROPELLER forum and to avoid being scolded, read the READ THIS FIRST sticky at the top of the forum. It tells you what you need to provide (much of which I just told you).