johnson 90hp performance curve

[jmlg]

Hi,<br />I am about to do some "fine tuning" of my hull+prop+engine during winter.<br />Do any of you know where I could find performance curve (rpm-hp-fuel consumption) of 90hp johnson oceanrunner on the net ?<br />I am looking for these curves because I am not sure to use the max potential of my engine. I don't reach WOT but I am afraid, with a lower pitch, to reach expensive fuel consumption.<br />Thank you for advising me,<br /><br />Jean.

 

[walleyehed]

Re: johnson 90hp performance curve

If you don't reach max RPM at WOT, you will NEVER reach max economy.It must have the correct prop to acheive max RPM. <br />You need to be able to obtain atleast 5800 with a normal load for the best performance and LONGEVITY of that engine.<br />There are many options as to "How" to increase performance, so if you'd post some set-up info, we can go from there.

 

[angus63]

Re: johnson 90hp performance curve

90 HP reached at appx 6ooo RPM depending on load.<br />Fuel consumption is about 9 gallons/hr WOT, and appx 6-7 gal/hr cruisin' at appx 4000 rpm. So many variables with each set-up. Best thing to do is create a baseline set-up and adjust one thing at a time and see if things get better.<br />Good luck

 

[walleyehed]

Re: johnson 90hp performance curve

HP is 90@ 5000RPM. Best economy is going to come with the combination that provides 5800 with a normal load at WOT. Fuel consumption will be the lowest at any given throttle setting in this case. If over-pitched, 15 gal/hr isn't out of the question at WOT.

 

[G DANE]

Re: johnson 90hp performance curve

Now I would like to know: Will it excede 90 HP at 5800 ?? My older 20 - 25 was marked 20 hp at 4500 RMP and 25 HP at 5500 RPM - sam blocks, I am aware there are differences in the motors, but do the powerheads put out higher HP at higher RPM's than at the certified point, or will they just do it burning leaner and cooler ?? Has anyone ever dynoed one ??

 

[walleyehed]

Re: johnson 90hp performance curve

Actually, on this engine, I believe the HP starts to drop off above 5000RPM, but I belive it's not a big enough drop to consider Zero gain above 5500RPM. Note the range on this engine is 4500-5500. Most people don't understand the engine should still turn 5500 for best results at any load, and in my mind 4500 was intended to specify a continuous cruise when propped for 5500. You and I both know the outcome of this outboard running at a max of 4500....it ain't going to last long...<br />Good to see ya still around, G Dane

 

[jimmbo]

Re: johnson 90hp performance curve

The 90 actually makes peak power @ 4800 rpm. at 5500 it is down around 82hp. The porting is too mild to allow good breathing above 5000, that plus the higher frictional losses as rpm goes up cause the engine to make less power than it does at lower rpm. If you want best top speed, prop it for 4800. Propping above and below this will, in most cases result in a lower top speed. WOT range is 4500 to 5500.

 

[walleyehed]

Re: johnson 90hp performance curve

I disagree with 4800...we already know this is not a good RPM on these. According to the book, the HP is 90@ 5000RPM as is, and has been standard for J/E engines for the most part.<br />jimmbo, where do you get the info on 4800??? Just curious..

 

[jimmbo]

Re: johnson 90hp performance curve

I saw it in an artical comparing 90hp motors in either Trailer Boats Mag or Bass & Walleye Mag. They dynoed the engines and reported where they made peak power. Both the OMC motor and the Merc inline 90 made their peak hp below the rated RPM. The Chrysler and Suzuki, being smaller engines did't make their rated power till they were closer to. I know the spec is 90hp @ 5000, but the 115, the 135, 125, and the 140, which were the same displacement were all rated at the same rpm. To make more power they have to spin faster, the 115 made its power at a higher rpm than the 90, and the 140 still higher.

 

[walleyehed]

Re: johnson 90hp performance curve

Interesting....But the engine in question is a 60 deg. looper, the other engines listed are all crossflows...completely different power bands.

 

[jimmbo]

Re: johnson 90hp performance curve

My mistake, I thought it was a crossflow.

 

[jimmbo]

Re: johnson 90hp performance curve

One thing that has always made me wonder.<br /><br />OMC/BOMB has made<br /><br />In 1965 90hp, 89.5 cuin 90hp@4500;<br />in 1968 85hp, 89.5 cuin 85hp@5000;<br />in 1969 85hp, 92.6 cuin 85hp@5000;<br />in 1981 90hp, 99.6cuin 90hp@5000;<br />in 1997 90hp, 113cuin 90hp@5000;<br />in 2005 90hp, 79cuin 90hp@5000.<br /><br />Do all these engine make about the same horsepower? I know the last two shown are prop rated while the earlier ones were crank rate.

 

[walleyehed]

Re: johnson 90hp performance curve

Never heard of a 113 cube 90...the later 90's and 115's are 105 cube engines.<br />From 95 to 98, you could get either crossflow or looper in the V4's. My 97 115 is 99 cube.<br />The 2005 90 is a tripple.<br />When they went to the 99 cube block, that's where the first power increase was noticable, and then again in 1995 with the 60 deg. looper.<br />Of course in 1985 when the bulldog 120-140 came out in big-block, looper form, they were real horses as well, but heavier.<br />I think one of the things we need to stay in contact with is the fact that NMMA allows a 10% max variation, whether up or down. It has been expressed in different ways by different people, but it boils down to the fact a 115 rated engine "Can" put out no more than about 120+/- 1 or 2, and it also (in the intrest of the manufacturer),can't be below 110+/- 1-2<br />BIA aloowed the full 10% in either direction prior to 85, so a 115 crankshaft rated "Could" technically be only 105HP but again, in the intrest of the manufacturer, they kept it as close to the actual rating as possible.<br />With the new NMMA certifications, a prop-rated 115 is in some cases within only a few HP difference. Best-case advantage in this HP class is about 8-10HP increase....not significant enough to add 6-8-10MPH. It just didn't happen that way.<br />Then we had evolution of the 60 deg. looper in this class (OMC) the torque curve provided higher ratings at a specified RPM usually 5000, but creates good torque ABOVE this figure.

 

[jimmbo]

Re: johnson 90hp performance curve

re 1997 90 displacemnet . I misread something in the brouchure<br /><br />I was wondering. did the 1968 85 actually put out more power than the 65 90hp given the displace ment and rated rpm? Also could the 1969 or later 85hp being 92.6 or 99.6 blocks put out more hp than the 1966-69 100hp which only used an 89.5 in block? Both rated at 5000.

 

[walleyehed]

Re: johnson 90hp performance curve

I honestly don't think there was much difference in the earlier versions without thru-hub exhaust...The props/engines from 69-up were thru-hub, and the ratios were different with a much better prop design, and yes, I think a 69-up 85 will outperform an early 100 mainly due to prop-style refinements, ratios and gearcase changes...Just more efficient over-all.

 

[jimmbo]

Re: johnson 90hp performance curve

Yeah the old 20:23 gearcase was kind of useless wasn't it? My dad had a 1965 90hp, it wasnt a very reliable engine, but it sure could suck back the gas. years later I had a Merc 90 inline 6, I swear it used less than 1/2 the gas the fat4 used. Went faster too!