WOT RPM for an Evinrude 115?

[fcards]

Hi everyone.

I have an 1978 Evinrude 115 with a 13 1/4 x 17 aluminum prop. My WOT RPM is 4400 and my speed is 27 MPH. I'm moderately loaded with 4 people on board. I was wondering what my WOT RPM should be, and what the idle speed should be on this motor? I'm new to boating, so bear with me and my "newbie" questions.

Thanks.

 

[Boilermaker]

Re: WOT RPM for an Evinrude 115?

Factory RPM range is 5000 to 5500 RPM with the horsepower rating of 115@5000rpm.
That said, many recommend running these engines much higher, in the 5800 to 6000rpm range, to reduce carbon build up around the piston rings.

Your RPM is seriously lugging the engine, causing undue strain & wear.
Has this engine always run in this range? Is the engine running correctly? Have you had it tuned & the carbs cleaned? What size boat is this on? Is the bottom of the boat clean?

I think you have some issues other then prop size ( unless this is a big heavey boat).
For comparison, I have a 1978 Johnson 115 (same engine) on an 18 ft 1971 boat. With a load of 3 adult men, a cooler full of ice, our fishing gear & 25 gals of fuel, my engine would turn 5200RPM @ 38mph with an aggresive 13.25 x 17" Stainless Steel prop... I changed that to a 13.25 x 15 S.S. to get some more rpms, and a faster holeshot.

 

[walleyehed]

Re: WOT RPM for an Evinrude 115?

May need to confirm tach is accurate as well..even though the speed is obviously low, the tach tells 90% of what the truth is..

 

[fcards]

Re: WOT RPM for an Evinrude 115?

Thanks for the info.

I'm not sure if the Tach is accurate, but after adjusting the trim, I achieved 31-32 MPH with about 5100RPM.

The boat is an AMF Crestliner Muskie Trihull. It's Fibreglass. The bottom is clean and I don't leave it in the water. Usually I have 2 of us on board, fishing gear and two 5 gallon gas tanks. Even with one tank empty, I haven't noticed a difference.

I think I should drop down 1 pitch size to maximize RPMs