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Discussion Starter #1
I was thinking ... I Bet a LOT of 2 strokes easily exceed thier Rated horsepower ;-)

Why else would a 25 year old 2 stroke eat a New 4 stroke for Dinner !!!

I have tried every known prop on a certin New 4 stroke and the same Hp 2 stroke with the stock prop kicks it's azz ...

Dave
 

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Many of the Japanese engines are under rated power wise. They don't like to rate in horsepower and go by displacement instead. One obvious example is the 20 HP 20.2 cu. inch two cylinder and the 30.3 cu. inch three cylinder rated at 25 HP. The 20 HP seems to move a heavier load than a 25 HP Johnson two stroke and the 25 HP seems almost immpossible to bog down with a 19' skiff like we mullet fish with. As for top end we just don't get into that as our boats are propped to move heavy loads rather than speed. I do like the 25 HP two strokes for the Gheenoe classic. (my old recreational boat set up).)

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Frank_S
 

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I was thinking ... I Bet a LOT of 2 strokes easily exceed thier Rated horsepower  ;-) 

Why else would a 25 year old 2 stroke eat a New 4 stroke for Dinner !!!

I have tried every known prop on a certin New 4 stroke and the same Hp 2 stroke with the stock prop kicks it's azz ...

                                                  Dave
Sorry but I gotta bring up all the back to back testing I did (on the same hull, the same day, etc.) between the 25hp mercs, both two-and-four stroke motors.

There is no difference. This is with a GPS.

I will agree though that some mfr's underrated their motors, I don't have a doubt about that. From what I've heard most rate at the crank, and there's been a few models/manufacturers that rate at the prop. That alone can be a good bit of difference.

-T
 

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I'm curious to know about this too.

I have a 1976 15hp johnson sea horse and I has been told that motor has a 15hp in the powerhead instead of the prop. It mean my motor wll be slow like a new 9.9hp 2-stroke?


All I know yamaha 25hp 2-stroke out ran any 25hp merc or johnson 2-strokes.

From my experience that new 25hp yamaha 2-stroke is fastest motor out there.....
 

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Blake, in a nutshell, yes.

http://continuouswave.com/whaler/reference/ICOMIA28-83.html

Right around 1983 they started measuring HP at the prop rather than the engine crank. There is a +/- 10% actual hp output though, could make some difference between engine brands.

I would assume a you are down 10% in power vs. a post 1983 15hp motor.
 

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In today's world of computer-controlled gizmos, EFI circuitry and using the same engine configuration for say 20, 25, and 30 hp engines (just an example) with just different programming, I HIGHLY doubt any manufacturer is going to give you more HP for your money when they sell a mechanically identical 30hp motor for a bunch of extra $$ as the 25hp.

-T
 

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Discussion Starter #8
Hopefully we can get someone to "flash" The "firmware" ;-)
 
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