corrrect prop pitch for a 85 Johnson

[Gbrettforever]

I have just recently restored an older 79 Vip runabout 16' with a 78 model 85 horse Johnson. I finally got the chance to take it out and see what she could do. It shot out of the hole and planed out great. mind you we had two grown adults in the boat total weight of both around 425 lbs. My rpm's were just a little above 5000 which I checked and that was just about right for the model. My problem was it didn't seem that I had much top end speed. I believe that prop pitch is 15 and I was just wodering if anyone had a boat or motor close to this model just to see what they would use. I have a stainless steal prop that also came w/ the boat but I'm not sure if it even fits. What I thought about doing was selling the stainless and finding a good aluminum prop possible with a 17 pitch. Any thoughts or ideas would be greatly appreciated. My plans for the boat are just to motor the wife and kids around the lake and maybe do some tubing. So I'm more interested in Fuel effeciency and top end speed, and not with getting out of the hole quickly.

 

[marinemech1]

Re: corrrect prop pitch for a 85 Johnson

your rpm range is 4500 to 5500 so your prop is a good fit

 

[moderator1]

Re: corrrect prop pitch for a 85 Johnson

5000 is too low for that engine...<br />With 2 adults and a normal load of other gear, you should reach 5500, other-wise with todays fuel, it will begin to coke-up.<br />When the manual was printed, the fuel quality was much greater and 4500-5000 was not an issue, now it is.<br />Stick with fresh 87 octane and get the R's up a bit.

 

[Dhadley]

Re: corrrect prop pitch for a 85 Johnson

A 15" prop on a V4 85 on a 16' boat seems way small. The holeshot should indeed be fantastic but the top rpms should be way more than 5000. Which in a way is good. For longevity youll be looking for 5800 as a target rpm with an average load.<br /><br />Lets verify the prop pitch and the tach setting. The tach should be on position 6. Make sure its an OMC / BRP tach or verify with one.

 

[Gbrettforever]

Re: corrrect prop pitch for a 85 Johnson

I'm looking at trying a prop with a 17 degree pitch to see how it reacts.

 

[moderator1]

Re: corrrect prop pitch for a 85 Johnson

17 pitch is going to drop RPM by 300-500 putting you in a really bad position if you want to keep your engine running.<br />If you don't have trim, you may have to move the tilt pin out one hole and try....there may be some other issues as well, but going to a 17 would be a mistake right now..

 

[Gbrettforever]

Re: corrrect prop pitch for a 85 Johnson

Thanks, I do have trim and the pin I'll look into other things first before trying the diff. prop.