Evinrude E-NATION, for those dedicated to water, power, fishing and fun
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Skipper
Posts: 5
Registered: ‎02-11-2012

What makes the horsepower difference with equal displacement?

[ Edited ]

Working with jet outboards, I'd like to get the most horsepower for the displacement.  I've got a selection of older motors from surplus auction, but some of the higher rated motors of the same displacement / frame size are not in the best shape.  For instance, I've got a great condition 25hp Evinrude that I've put a jet on, but the performance is sluggish, and I've got a 35hp older Johnson that looks bad, but might give me better performance with that same jet unit.  I haven't put the jet on it, and I'm not sure I want to yet.  Maybe I could just transfer some parts to accomplish what I want.

 

Would the difference in horsepower just be in the carbs?

   

What makes the difference in horsepower between the 20-35hp 31.8 cu. in. 2-cylinder engines?  

 

Would that hold true also for the 40-60hp 44.99 cu. in. 2-cylinder engines?

 

Long live natural aspiration!

Admiral
Posts: 8,432
Registered: ‎07-14-2011

Re: What makes the horsepower difference with equal displacement?

Each  year there may be various internal changes within motors of the same family regarding horsepower output compared to previous years. Most often the differences consist of reed boxes, carburetors, exhaust tuning components, cylinder heads, and cylinder porting. Some motors, especially the highly tuned versions, may also have a different rpm power rating and operating range.

 

The best way to find out any differences is to go to www.shop.evinrude.com and choose the appropriate Johnson or Evinrude models in question and compare the parts changes between the horsepower ratings of the same displacement motors.

 

 

 


"There is never just one thing wrong with a boat";
                    -- Travis McGee, main character in a book series by John D. McDonald 


 



***************

The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.

The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.


Skipper
Posts: 5
Registered: ‎02-11-2012

Re: What makes the horsepower difference with equal displacement?

[ Edited ]

Hi Bill,

 

Well, I took your advice and here's a puzzler:  I went through all the parts for the 1990 30hp and 35hp models and could not find one single part that was dedicated for the 35hp model only, except the decal plates.

 

I guess there's something I'm missing.  Was a 35hp model even sold in 1990?  I found an old brochure that doesn't list it, but I see model E35RLESS listed in all the parts catalogs.  Here's a shot of the brochure:

 

http://rides.webshots.com/photo/259363428010135459​0wqDYjU

 

There's a clear distinction in parts between the 20/25 and the 30/35, some of which is structural in the midsection.  Power-wise, there's even a difference between the 20 and the 25 carburetors and intakes.   The reason I'm focused on this year is that I have an E30RLESS prop and the jet converted motor I have is an E25RESB.

 

What's strange is that between the 30 and 35, at least in that year, it looks to me like they are the same motor with different decals and model numbers for no apparent reason.  Could my 30hp motor be capable of making 35hp?

 

Could a turn of a screwdriver make the difference between 30 and 35hp ratings, or was there really none except possibly for marketing purposes?  I'm starting to think that I could get another 7hp out of my 25 jet with just a carb. and intake swap with that 30hp I have that may really be a 35hp in disguise.  Then I'd be around 25hp at the jet, rather than 18hp, which could make a good bit of difference.

 

Thanks for your help!

Admiral
Posts: 8,432
Registered: ‎07-14-2011

Re: What makes the horsepower difference with equal displacement?

A screwdriver will not add 17% increase in power to a 30hp outboard.

 

Those motors were built 22 years ago by a company that is no longer in business. Sorry to say any  info about minute differences is not easy to find except through the parts book.

 

 

 


"There is never just one thing wrong with a boat";
                    -- Travis McGee, main character in a book series by John D. McDonald 


 



***************

The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.

The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.


Skipper
Posts: 5
Registered: ‎02-11-2012

Re: What makes the horsepower difference with equal displacement?

Perhaps the parts sold for replacement now are not as distinguished as they once were.  I went through the online parts list in minute detail and that's what left me scratching my head.  No dee france between the 30 and 35.

 

You had mentioned tuning and porting, so I thought there could have been some difference made just by how things were assembled and adjusted.  Something has to account for that 17%. My Seloc manual doesn't cover a 35 model either, it only has the 30hp listed like the old Evinrude brochure.  So it seems like the 35 was special somehow.

 

The real head scratcher is this:  the cover for that motor I have has a plate in the front that says 35 and one in the back that says 30.  The motor was secondhand to me, but I think it was from the factory that way.  The model number though, indicates it's a 30.

 

I guess only an OMC engineer with a good memory from those days would know for sure what's up with all this ambiguity, but now I'll have to see if I can hunt down the actual factory parts list issued back at that time just to satisfy my curiosity. 

 

You're not kidding it's not easy, but at least it's entertaining when it gets this mysterious.

Admiral
Posts: 8,432
Registered: ‎07-14-2011

Re: What makes the horsepower difference with equal displacement?

Actually they can be the same engines and parts. The hp rating tolerance is plus or minus 10%. That means a 30hp can be from 27hp to 33 hp and a 35 can be a 31 1/2hp to 38 1/2hp. So you can see that both in the 31 1/2hp  to 33hp  range, the allowable rated hp will overlap. I think this solves your mystery.

 

 

 


"There is never just one thing wrong with a boat";
                    -- Travis McGee, main character in a book series by John D. McDonald 


 



***************

The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.

The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.


Skipper
Posts: 5
Registered: ‎02-11-2012

Re: What makes the horsepower difference with equal displacement?

[ Edited ]

This overlap in tolerance allowed for a hp rating is somewhat along the lines of what I was thinking also.  In terms of marketing, I was thinking that a motor sold as a 35 would have to verified - or assembled by the "A" team - in order to be guaranteed to be in the upper range of the tolerance.  I would imagine a premium would be charged for that higher rating.

 

If the nominal hp for these assemblies was in the lower- mid 30's, you still may get some that wouldn't make the cut for rating at least 31.5hp - otherwise why not sell them all as 35's?.  It would just be easier to sell most of them as 30s rather than verify them all as 35s.  I'm just guessing that a factory load test and a few extra dollars may have been required to get that 35RLESS model sticker put on rather than the 30RLESS.  This is where it seems like some extra care in machining and assembly could make the difference.  It also seems like there's probably a good chance there'd be no difference between my 30 and a typical 35 of that year - except that someone got charged more for that 35.