Question about hp ratings old -vs- new

[606WPD]

I have an older (1985) Evinrude 25 hp outboard on my small pontoon. It runs great and I'm satisfied with the performance but I don't like the noise and am thinking about getting a new 4 stroke.

Long story short, I keep reading that they rated hp differently back then compared to how they rate it now. Does anyone have any idea what I would need in a new 4 stroke to equal the performance/hp rating of my '85 two stroke.

Thanks guys.

KPC

 

[Barramundi NQ]

Um....hp ratings haven't changed, if you buy a new 25 hp 4 stroke it will as rated, a 25hp. It will however be a little heavier. This is because 4 strokes have more components and require oil in a sump. With 25 hp you may notice the difference in performance because of the power to weight ratio change. Maybe you should consider going to a 30 or 40 hp to completely compensate for the difference. That's assuming that your transom or motor mount will be able to take the extra weight and power.
my 2 cents

 

[Scott Danforth]

prior to the mid 80's motors were rated at the flywheel. post mid 80's they were rated at the prop. your 85 should be prop rated

 

[606WPD]

Thanks Barramundi.

I was under the impression that with the newer outboards, hp is rated as actual prop output, and the older ones were rated at the engine, therefore not accounting for any loss trough the shaft and gearcase.

KPC

 

[Barramundi NQ]

I stand corrected.

 

[606WPD]

Thank you Scott.

KPC

 

[Frank Acampora]

In 1984, the NMMA decreed that all outboards should be rated by horsepower delivered to the prop. Thus your engine is prop rated. Because a 2 cycle engine has one power pulse per revolution and a 4 cycle has one power pulse every two revolutions, given the same displacement and number of cylinders a 4 cycle engine will have less torque at low end. At full throttle, horsepower is horsepower so for equal horsepower rated engines, the top speed should be about the same. The difference is the 4 cycle will take a bit longer to get there. For a slow moving party boat, you really can't beat the quiet running and lack of oil cloud of a 4 cycle engine.

If definitely going 4 cycle engine, you may want to step up 10-15 ponies. After all--Too much horsepower is never enough. And no one says you must use it all.

 

[606WPD]

Thank you Frank, sounds like good advice.

KPC

 

[pckeen]

Although the ratings were calculated differently, my understanding is that there isn't a significant difference in terms of power between a 25 hp engine 30 years ago, and a 25hp engine today. This is with the caveat that different engines will have different levels of torque at low end , but that is true for comparing different new 25 hp engines from different manufacturers today. In terms of power on your boat, if you were happy with your old 25hp, you'll be happy with a newer 4 stroke 25 hp today.

Check the maximum rated hp for your boat - that will tell you the most power you will want to put on it.

Be aware that if you are replacing the engine with a new one, you are likely to have to replace controls and perhaps steering components as well.

 

[steelespike]

Buying new; a 25 or 30 direct injection 2 stroke will have more low end power, fewer moving parts and fewer and less complicated service intervals.
also The Evinrude Etec does not require a break in period,and I believe no service required for 3 years or 300 hours.