What is the operating range for my 1980 115 Johnson?<br /><br />I am currently running a 17 pitch and getting 5200 RPM at WOT in slightly choppy water. The boat is a 16ft run about.<br /><br />Stephen
You are doing fine at that rpm. The factory recommendation is from 5000 to 5500 rpm, since they suggest propping the engine in the upper half of the operating range.
5200 rpm is almost good trim the engine to the propper angle and it will go up for 2 or 3 hundred rpms more.<br />do not go smaller with your prop. <br />did you get a new prop?<br />check the throttle cables.<br /><br />reeldutch
We find that the rings coke up less and therefore the motor lives longer if its capeable of 5800 with an average load. <br /><br />I wouldnt change props. We prefer to gain rpm with set up. That way your overall performance will increase. Try raising your motor (increase your X dimension) to reduce drag. Let us know what you find.<br /><br />Good luck!
What is dimension X?<br /><br />The motor is set as far down as it can on the mounts. How much should i lift it at a time? Will this actually make a difference?<br /><br />Stephen
Dhadley,<br />I have the same issue with my 1980 rude 50hp. I was told by the rude dealer that my wot rpm range was 4500-5500. Are you suggesting that that range is a little low and I can run up to 5800 as you suggest for Matysiak?<br /><br />Matysiak, <br />I don't want to take away from your question but we are in kinda in the same boat so to speak. I can get 5600 out of mine with a light load though.
It may suprise you how much difference it makes. Any part of the motor in the water creates drag. We try to eliminate as much of that drag as possible. Your limiting factors will be the style of prop you have and the motors ability to still maintain water pressure. Obviously hull design has something to do with it too.<br /><br />Raising the motor costs almost nothing. A little tube of Boat Life calking is about it. A tach and water pressure gauge is a must but thats standard equipment nowdays.<br /><br />Dave, yes we like to see motors like yours in that range too. They like rpm so perhaps even a tad more wouldnt hurt.
Thanks. I think I need to raise the motor one more notch. I should then be able to get that rpm. Currently the plate is about 1/4"-3/8" above keel. An inch may be just right.
So any way that you can achive it, the RPM's need to come up. I think that's where I was headed with it, but Dhadley has the right starting point. And if that doesn't get it, then prop away... Cause 5200 is lugging it...
Matysiak <br /><br />You didnt mention your speed anywhere. It seems like a 115 should be turning a 17" pitch on a 16' boat quite easy, unless the boat is heavy. OMC prop reference chart advises propeller choice at start at 19" pitch for 17-20' light runabout at speeds 38 - 50 mph ( which is a wide span though ). Are you sure tach is ok ? Have you measured your speed by GPS ? But it seems reference chart usually advises to run lower rmps than later experiences showed were good.
