Outboard HP Ratings

[rjezuit]

I have heard that at some point in the past(I don't remember when) that manufacturers started rating their motors differently (at the prop versus at the powerhead?). If this is true, what would be the difference between a 18HP from 1957-1958 and an 18HP from the late 60's. Or for that matter the difference between the power of a 1956 15HP and a 1967 20HP. Is it really 5HP or is it more or less? thanks, Rick

 

[tashasdaddy]

Re: Outboard HP Ratings

the change came in the 1980's. the older motors were rated at the power head.

 

[wbeaton]

Re: Outboard HP Ratings

I've read lots of different numbers, but it seems the difference between powerhead and prop ratings are in the neighbourhood of 10-15% on these little motors.

 

[rjezuit]

Re: Outboard HP Ratings

So I would be getting a true 5HP between the '56 15HP and a '67 20HP. For the same weight, seems a good choice. Can anyone tell me if there are any known issues with late '60's 20HP Johnson/Evinrude motors? Thanks, Rick

 

[NelsonQ]

Re: Outboard HP Ratings

So I would be getting a true 5HP between the '56 15HP and a '67 20HP. For the same weight, seems a good choice. Can anyone tell me if there are any known issues with late '60's 20HP Johnson/Evinrude motors? Thanks, Rick

Yes you should be seeing a difference of 5HP assuming they're both in good running shape (no lost compression, etc) but a fair comparison.

I don't know anything about the late 60's Johnson/Evinrude motors (had a 65 Merc) but from what I've seen lately is the only real issue is the lack of them for sale. Apparently very well built motor and when well maintained, will last forever. (I'm looking for a mid 60s-80s motor myself to work on and rebuild)

 

[Chinewalker]

Re: Outboard HP Ratings

The 1956 15hp is giving up a couple cubes to the 18/20hp models, as it is a hair less than 20 cubic inches, while the 18/20/25 up to about 1976 were a hair over 22 cubic inches. The late 1960s 18 and 20 were virtually the same. I think the only difference that I've ever seen between them was the 20 had the reed stops opened a fraction of an inch more. The 25hp had more differences inside, as it used different pistons and cylinder head.
- Scott

 

[rjezuit]

Re: Outboard HP Ratings

Thanks for the input. The '56 15HP I have now scoots along pretty well with only me aboard, but only gets up to around 16-17MPH with me and my 2 girls aboard. Add the wife and I am down around 11-12 best case. I added a SE200 hydrofoil which helped a lot to get to these numbers, prior to that with me and the girls, I ventilated badly and could only get around 12-14 MPH. The foil took care of the ventilation totally, but I would like to see 18-20 with all 4 of us aboard. There's a '67 20HP Seahorse on the local craigslist listed for $475, I might look at. Rick

 

[cc67]

Re: Outboard HP Ratings

I have several motors from the 50s and 60s in those HP ranges. You will notice a lot of difference between them. My 54 15hp Evinrude is a strong running motor but is no match for my 18-20 hp models.

 

[Chinewalker]

Re: Outboard HP Ratings

The 20 should have noticeably more grunt - no substitute for cubic inches... This assumes it is healthy with good compression and correct prop...
- Scott

 

[eavega]

Re: Outboard HP Ratings

I have a 68 Johnson 20 HP, and as far as I can tell the thing is bullet-proof. Even with what I suspect was marginal maintenance before I got it, the motor still has good compression numbers and has a whole lot of giddy-up for its 80 Lbs of weight.

-Eric