Just curious, how are/were motors rated?

[mr-asa]

I was talking motors with a friend the other day and going over the gains I expect to get from modifying my Ford. I remembered that it originally had a rating way way above what it actually produced at the wheel. The difference between SAE and Net HP ratings, basically.

Was there ever anything similar for outboards? Based on the stories I’ve heard of how the (I wanna say) early Mercury exhaust manifolds for the racers were developed, I have a hunch that there might have been something like that going on.

[wiscoboater]

Back in the 50’s and 60’s Mercury under rated the HP output of most of their motors. Kind of Carl’s way of "cheating" the system in the racing circuits. Outboards were rated at the powerhead until sometime in the early 80’s I believe but dont remember what year that changed to rated at the prop shaft. About a 10% to 15% difference in rated HP when measured at the shaft. If you want a real view as to what was going on in the outboard world read the book Iron Fist. It’s a real eye opener to how competitive the market was and the lengths one mans company went to to game the system.

[dave-bernard]

outboards back then were rated at a certain RPM. that is were merc got the advantage. a KG7 was 10 hp at 4000 RPM"S but would run at 6000 RPM’s thus putting out more like 16 hp or so.

[vintin]

In an older issue of the Antique outboarder I remember reading the 25hp RD put out 28hp and the 35hp RD put out 33hp. Maybe that is why in the 1960’s those motors got those power ratings. Explains why that 25hp RD does so well, too.

[garry-in-michigan]

In the dawn of the industry, horse power was assigned by guesstimation. Some companies used a pound scale tying the boat to the dock to measure motor thrust. It was found to be more of a propeller efficiency test than a measure of horse power. As outboards became popular a test propeller with a flat outer rim was put on the prop shaft and an adjustable band which was attached to a pound scale was put around it. (Thus the term "Break Horse Power".) The first dynomometer. When it was found horsepower sold motors, engineers went to great lengths to be sure there carefully hand built prototypes put out the most horse power possible. The production line could not afford to be as meticulous. The casting and machining of that time produced motors of varying horse power. Few achieved the rated power, and a few were downright lemons.

Things came to a head in the early thirties when customer complaints and charges by rival companies caused Steve Briggs to get together with other manufactures (Evinrude, Elto, Lockweed, plus Caille, Johnson, Scott Atwater, Muncie Gear Works and others) formed the National Outboard Association. It was agreed that representatives of rival companies would randomly pick three models off the line to be sent to the Pittsburgh Testing Laboratory and the average horsepower of the three would be the certified horse power of that model. They measured the electrical output of an electric motor attached to the propeller shaft. It is considered more accurate. Overnight some Evinrudes lost 2 or 3 horse power.

Later Champion and Martin joined. When Mercury was asked to join, they got a "No, thank you" from Mr. E. C. Kiekaefer. His wildly inaccurate horsepower ratings coupled with increased sales spelled the doom of the NOA. Evinrude always bought rival manufacturers outboards for Engineering to examine. I wish I still had the horse power curves they produced for Mercury outboards. Today the brass NOA certification medallions that hung on all Evinrude and Elto outboards of the late 30s and 40s are considered collectors items. The horsepower of the classics of the 50s we love were the best estimates of the engineers at the time the owners manuals and advertising campaign were laid out. . . 😀

[pm-t2]

How are motors rated????

My stuff is primo, the best runners anywhere.

anybody else’s stuff is sub-standard.

Hope this answers your question, lol

Best,
PM T2

[chris-p]

As usual Garry, great information!

[garry-in-michigan]

The Horse power curves produced by engineering were considered "Top Secret" and to be shared with no one. Evinrude was afraid it would add to Mercuries sales. Steve Brigs said let them have the crazy racers, we will go after families and fishermen. We will sell more motors and more dependable motors. That changed when Ralph Evinrude brought Charlie Strang on board. No one ever made money on racing, but it was good for testing dependability and good advertising. I see a lot of those old "crazy racers" enjoying there classic Mercuries at our meets today. . . 😎

[outbdnut2]

I’ve got an old 2-page magazine ad for the Johnson line from 1957 that claims all HP that year was measured at the propshaft. Not sure what they used to measure it.
–
Some years later, OMC and Mercury all went to the engine block to measure it on most models and in the mid to late 1980s, models went back to the propshaft measurement to compete with motors from Japan, and that’s why the 9.9 Mercs (1986 up) and 9.9 Johnsons from somewhere in the late 1980s up will run circles around their 9.8s and 9.5s, and even the early 9.9 Johnsons, before they added tuned exhaust to boost HP.

[jeff-register]

I think it was Yamaha outboards that was the first prop rated horsepower to hit the market. Reliable? I’m on my second 1954 Evinrude Super Fastwin only because I sold the first. Both motors always start & run very well & continue to do so just like my 58 Johnson 18. Never seen another vintage motor idle so well!

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