1987 Evinrude 120 rpm at wot

dk47

Cadet
Joined
Aug 23, 2010
Messages
6
I have a 1987 120 evinrude that runs perfectly. Noticed the rpm's at wot were around 4900 with a 13.2x19 aluminum prop. Installed a new 13 7/8x17 viper ss. Now at wot its 5900. I'm satisfied with the performance but need to know if that's to high. Can't find the rpm range anywhere. I have been told it depends on which power pack you have, so how do you know? Thanks for any help.
 

smokeonthewater

Fleet Admiral
Joined
Dec 3, 2009
Messages
9,838
Re: 1987 Evinrude 120 rpm at wot

I think 5900 is pushing it a wee bit but no reason you can't back off the throttle just a bit.
 

limitout

Banned
Joined
Oct 1, 2013
Messages
543
Re: 1987 Evinrude 120 rpm at wot

im going by very old memory here but I used to have some old evinrude service manuals and if I recall correctly the johnson/evinrudes all use the 5200-5800 rpm range from 85hp thru 135hp motors.

back in the 1980's I had an 88, a 90, and a 135 and they were all propped to run 5600rpms
 
Last edited:

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: 1987 Evinrude 120 rpm at wot

Operating range is 5000-6000 rpm. according to specifications in factory service manual.
You might verify your tach is accurate. Borrow or rent a shop tach. Or get us your boat size, gear ratio and the wot rpm and gps speed lightly loaded.
 

dk47

Cadet
Joined
Aug 23, 2010
Messages
6
Re: 1987 Evinrude 120 rpm at wot

The boat is a 17ft Sailfish Center Console, not sure about gear ratio but it has the 13 spline prop shaft if that helps. WOT with this 13 7/8x17 viper ss is 5900 at 42 mph, by gps. Like I said, thats plenty fast for me, I just don't want to over rev the engine.
 

V153

Lieutenant Commander
Joined
Apr 16, 2011
Messages
1,764
Re: 1987 Evinrude 120 rpm at wot

Just use good gas & oil. Don't run it all day at 5900 & you'll be fine.

I've wound them up to 62-6300 for short bursts with no ill effect.
 

SkiDad

Lieutenant Commander
Joined
Jul 18, 2010
Messages
1,518
Re: 1987 Evinrude 120 rpm at wot

i don't see an issue at all with 5900
 

limitout

Banned
Joined
Oct 1, 2013
Messages
543
Re: 1987 Evinrude 120 rpm at wot

i don't see an issue at all with 5900

have to agree, if the specs call for a range of 5000-6000 then at 5900 you are perfect because you want to be as high in that range as you can get without going over it
 

V153

Lieutenant Commander
Joined
Apr 16, 2011
Messages
1,764
Re: 1987 Evinrude 120 rpm at wot

Correct. They just start makin' hp at 5000 or so. RPM = hp with these motors.
 

MikeB0307

Petty Officer 3rd Class
Joined
Jul 13, 2012
Messages
88
Re: 1987 Evinrude 120 rpm at wot

We ran our '89 150 at 5800 a good bit and never had an issue.
 

phillnjack2

Ensign
Joined
Apr 30, 2011
Messages
918
Re: 1987 Evinrude 120 rpm at wot

that engine will run all day every day at 5900 and will last longer than running it at under 5000 that is labouring it.

you have the perfect prop for that boat engine set up, the old ali prop was probably bent out of shape.

42mph is perfect and well fast enough.

enjoy the boat.

.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,544
Re: 1987 Evinrude 120 rpm at wot

My 50+ years of experience with 2 cycle engines is that they love to run and get real mad at you if you lug them. Agree run good oil, I like Pennzoil Premium TC-W3 which is semi-synthetic. Runs clean and very little smoke. WW sells it at a good price. I run my Mercs over the "red line" all the time, reasonably short birsts 3-5 minute sprints, not all day, and they love it. Never have blown an engine from running the rpms too high. My personal preference is to run a fuel additive which I learned of on this site half a dozen years ago. Called Sea Foam. Most all auto stores stock it including WW. Read on the label for usage and their guarantee.

Mark
 
Top