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Author Topic:   Horsepower ratings
skookum point posted 05-15-2001 12:33 PM ET (US)   Profile for skookum point   Send Email to skookum point  
From time to time it has been mentioned that the older outboards were measured with a different horsepower rating system. If I understand it correctly, the new motors are measured at the prop and the old motors are measured at the powerhead, right?
My question is, when did they make this change? Does anyone here know?
jimh posted 05-15-2001 08:40 PM ET (US)     Profile for jimh  Send Email to jimh     
I don't know the exact date when the horsepower ratings changed, but I imagine it must have been the result of some federal legislation requiring it.

I think there were also requirements about the accuracy of the ratings, too. Makers have a certain leeway. For example, you can have an engine that produces, say, 68 HP and call it a "70", and also have an engine that produces 72 HP and label it a "70". But I don't know what the exact leeway allowance is.

It used to be a practice in the industry for certain makers to underrate their engines, so a 20 HP of a certain brand might really be more like a 27 HP engine. Mercury, I think, was infamous for this. It was a marketing ploy on their part, tending to create the impression that a Mercury engine was faster than other brands.


Tsuriki BW posted 05-15-2001 09:20 PM ET (US)     Profile for Tsuriki BW  Send Email to Tsuriki BW     
Heard that the reason 9.9hp motors were labled that way was for insurance purposes for rentals. 10hp or more resulted in a higher rate so mfgs labeled them 9.9.

Many are just a slight mod away from a 15hp.


Dick E posted 05-15-2001 09:33 PM ET (US)     Profile for Dick E  Send Email to Dick E     
OMC went to prop rating in 1986.
There is a 10% leeway in defining hp
For example Merc's 4 stroke 90 hp is actual 96 hp while Yamaha's 100 hp 4 stoke is the same powerhead at 96 hp too.
Same powerhead one labeled 90 hp and the other 100 hp.
Now when you get to 200 hp that 10% can really mean something.
Dick E
fester posted 05-16-2001 01:18 AM ET (US)     Profile for fester  Send Email to fester     
Is there a significant diference in measuring the horsepower at the powerhead verses the prop? It would seem obvious that measuring horsepower at the prop would lower the horsepower rating of the motor in that some power would be lost with the operation of the water pump, lower unit, etc. But how much power is lost and how does this affect the horsepower rating of an older boat when one is repowering with a new engine? What is my 1979 175 horsepower Evinrude equivilent to when comparing it to a new motor?
skookum point posted 05-16-2001 02:34 PM ET (US)     Profile for skookum point  Send Email to skookum point     
Thanks Dick E, that's good news and exactly what I wanted to know. My OMC is a 1987 model.
Dick E posted 05-16-2001 06:41 PM ET (US)     Profile for Dick E  Send Email to Dick E     
fester your 175hp engine is equivlent to about 150 hp engine today
Chesapeake posted 05-17-2001 01:32 PM ET (US)     Profile for Chesapeake  Send Email to Chesapeake     

How would a 1975 85HP Johnson compare with a 2001 Yamaha 90HP 2-stroke? Would appreciate your insight.


Eric posted 05-17-2001 05:01 PM ET (US)     Profile for Eric  Send Email to Eric     
I've seen a couple of postings where the 90 Yamaha is said to be making less than rated horsepower. I've got a 99 model Johnson 90 (carb, not ficht). Anyone have any idea where these are in the power range? The input I get from the mechanics is that they have a pretty good output.
Pat Smith posted 05-17-2001 05:06 PM ET (US)     Profile for Pat Smith  Send Email to Pat Smith     
I have an 150 hp Johnson (1985)two-stroke on my 18ft Outrage,so if I put a new four-stroke 115 hp,it would be about the same?Pat
NWflyfisher posted 05-17-2001 07:05 PM ET (US)     Profile for NWflyfisher    
Dick E,

If a modern day engine was measured at the powerhead and then measured again at the prop, would that still show such a dramatic (25hp) change in the hp rating as you noted for Fester's comparison on his outboard (175hp his to 150hp modern day?) Do you know offhand which method is used to measure the hp in tow vehicles? Now I know why my local marine mechanic keeps referring to my 1978 Mercury 700 70hp as a "Merc 60." Thanks for the enlightenment.

Tom W Clark posted 05-17-2001 09:38 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
Rated horse power is an inexact science. I had an 18 Outrage with an '83 Johnson 150 (powerhead rated) That boat was stolen. I got the boat back minus the motor so insurance bought me a new '90 Johnson 150 (prop shaft rated) The original motor was every bit as fast, if not faster than the new motor. I cannot quantify this statement as I only ran the original motor on two or three occasions before it was stolen. But I know it was every bit as fast because I remember a slight disapointment when the new motor was rigged and I started running it. There was no difference in top speed.

I know some motors will be faster than others. This is true of cars as well. A lot depends on how they are broken in, how they were built in the factory, and just the alignment of the stars....

jimh posted 05-17-2001 11:16 PM ET (US)     Profile for jimh  Send Email to jimh     
Regarding the rating of outboards at 9.9 HP:

I think this resulted from some laws in certain midwest states that exempted boats from registration if they were powered by less than 10 HP engines.

Dick E posted 05-17-2001 11:42 PM ET (US)     Profile for Dick E  Send Email to Dick E     
An engine measured at the powerhead vs at the prop will be APPROXMATELY 15 % less at the prop.
In addtion MFG can rate their engines 10 % + or - from actual horsepower.

Mercury has been known through the years to push the 10% limit, but today eveyone wants to be the fastest.
So in theory a pre 1986 OMC outboard could be 25% less hp then todays model.

Chesapeake, I would say that Yamaha is about 10- 15 hp stronger then that Johnson.
Pat, I would say you need about 130 hp to make it close.
NW I have no idea how tow vechiles hp is measured.

Hank posted 05-18-2001 12:23 AM ET (US)     Profile for Hank  Send Email to Hank     
The Manual for my 1984 90HP Evinrude states, under specifications:
Power at Propellor Shaft According to ICOMIA 28-83... 90HP (64.0kW) Rated at 5000RPM

Full throttle operating range..4500-5500RPM

Note that rated power is at PROPELLOR SHAFT in 1984 . Also note that power is rated at 5000RPM while WOT RPM can be any where from 4500 to 5500 RPM


Lil Whaler Lover posted 05-18-2001 07:22 AM ET (US)     Profile for Lil Whaler Lover  Send Email to Lil Whaler Lover     
Every year "Bass and Walleye Boats" magazine does some detailed comparison testing of outboard motors. In the April 1997 issue they compared the 7, 90 horsepower engines then on the market. Each motor was run on one of three identical Crestliner 1750 Fish Hawks. While not Montauks, they are good hulls to compare the motors on. For each motor they test dyno horsepower and dyno torque numbers, and list the rpm where the maximum is obtained. The following are the results:
Force: 83 hp @ 4800, 104 lbs of torque @ 3300, 40.8 mpg, 5.8 max mpg.
Mercury: 92.6 hp @4800, 104 lbs of torque @ 3000, 42.6 mph, 5.4 max mpg.
Nissan: 91 hp @ 5200 rpm, 103 lbs of torque @ 4150 rpm, 41.5 mph, 5.4 max mpg.
Yamaha: 91 hp @ 6000 rpm, 101 lbs of torque @ 3800 rpm, 39.9 mph, 5.6 max mpg.
Johnson: 91 hp @ 5200 rpm, 116 lbs of torque @ 3000 rpm. 43.0 mph, 5.0 max mpg.
Suzuki: 105 hp @ 5500 rpm, 114 lbs of torque @ 4400 rpm, 41.0 mph, 5.1 max mpg.
Honda (only 4-stroke): 91.2 hp @ 5800 rpm, 101 lbs of torque @ 4000 rpm, 42 mph, and 6.2 max mpg.

The article stated that all engines ran well on the Land and Sea dyno except the Suzuki which did not hhok up well and had some electrical problems when hooked up. Sand and Sea said its dyno worked right, Suzuki said its engine did not develop that much power. real world performance placed Suzuki in the middle of the pack.

Interesting the big block 2-strokes really do put out the torque. Look at Johnson's numbers. But as usual Mercury wins the horsepower race. Dave

Peter posted 05-18-2001 07:53 AM ET (US)     Profile for Peter  Send Email to Peter     
I have ridden in a Montauk with a Johnson 90 (60 degree block) and it truly is a torquey motor. If you don't hold on tight when the boat is punched up on a plane, you'll be out over the transom in no time.
Eric posted 05-23-2001 11:36 AM ET (US)     Profile for Eric  Send Email to Eric     
Interesting numbers from the magazine comparisons. Note the the motor with the most torque was the fastest.
triblet posted 05-23-2001 12:15 PM ET (US)     Profile for triblet  Send Email to triblet     
I have an Evinrude 90 of the same vintage,
and is the same as the Johnson except for
the paint job (same p/n for the service
manual, and no J vs. E differences in the
service manual). And yes, it has stump
pulling torque. Mash the throttles and
folks in the rear facing RPS can land on
their butts. Guess I thought most outboards
were that way.


jimh posted 05-23-2001 09:39 PM ET (US)     Profile for jimh  Send Email to jimh     
I'll have to throw this story into the ring:

This winter we were fortunate to be aboard lhg's WHALE LURE, cruising a few miles offshore in a calm Atlantic. My wife, Chris, was at the helm, I was helping her with the throttles, and lhg was in the rear of the cockpit.

Chris was getting the feel of the boat as we cruised along at about 3,000 RPM. After a few minutes she was ready for a bit more speed, so she asked me to give it a bit of gas. I gave the dual controls a little nudge forward.

The twin 200-HP counter-rotating Merc EFI's on the stern bracket instantly jumped to around 4,000 RPM. The big Vengence props had a firm bite, and the boat accelerated immediately to about 15 MPH faster.

Out of the corner of my eye I saw lhg go flying sternward, just catching himself as he reached the transom.

Larry came back to the console and gently reminded me, saying, "Hey, you gotta TELL me when you're gonna do that!"



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