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Evinrude 70 prop selection

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Nick0151

Regular Contributor
Hi all after few hiccups with my 82 evinrude 70 it’s finally running as it should be.

took it out yesterday and with 5 people (2 adults and 3 kids) picnic items a dog and 50L of fuel onboard, would get up to just over 30 on the gps and would rev to 5800 and still had little left with the spark advance, it’s over what it should says 5500 max rpm but not to bothered about that as seen ppl say to go over slightly.

question it’s running a 13.75 15 prop at the min do you think if I prop it to a 13 21p it would be ok for the rev range it’s on a light shallow V hull boat like a fletcher but it’s a concord fiesta. It gets up onto plane in about 10/15 secs at the moment.

thank you in advance

nick
 
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I read my have understood it incorrectly says every inch up in prop you go up you lose 150/200 rpm then every 1/4 inch of diameter you drop you gain the same I guessed about that would give me about 5500 max rpm
 
Guys sorry to bump post up but really like some advice not sure if should go with:
13 19p
13 21p

boat performs like in video above with
13.75 15p would rev to about 5800 ish

Thanks

nick
 
Nick0151 said:
Guys sorry to bump post up but really like some advice not sure if should go with:
13 19p
13 21p

boat performs like in video above with
13.75 15p would rev to about 5800 ish

Thanks

nick
Click to expand...
Hey Nick,
In most applications the 70HP engines perform very well with a 13 1/4 x 17P prop. In general, each 1" change of pitch results in 200RPM difference. So, if you went to a 17P you should see about a 400RPM drop which would put you right in the correct range.

If you felt you had a little extra throttle left at 5800RPM you might consider getting a cupped prop. Those will bite the water a little more and sort of act like another 1/2" of pitch or a little more and will change your RPM by maybe another 100-150RPM

You definitely DO NOT want to go to a 21P. That will drag you down to under 5000RPM for sure and a 19P is probably a little too tall as well. If you go to a 19P you'll likely need to drill vent holes in the prop to help with hole shot. You may find you'll want vent holes in the 17P as well just to maintain good holeshot performance.

I'd suggest going to a local shop or browsing marketplace or Ebay to find a used 13 1/4 x 17P aluminum prop for a decent price. Give that prop a rip in multiple water conditions and loading configurations and see how it performs.
The main thing is you want to prop the boat for your maximum, most commonly encountered max conditions. If 5 people and a full tank of fuel is a typical day on the water then test your props with that load in the boat. If you're still over 5500 RPM at full load with a 17P then find a good 19P and try that. But, if I had to guess I'd say the 17P is going to be your sweet spot.

KJ
 
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