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year of HP ratings change. prop VS. crank

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  • year of HP ratings change. prop VS. crank

    what year did they start rating the HP at the propshaft instead of the crankshaft.i ask this because i am looking for a new motor(to me) and dont wanna get a 1985 70hp if a 1986 70hp is gonna be more power.... i use those figures as examples only... not... i cant post that i wanna buy a 70hp motor or ill tick off JB... hint hint

  • #2
    Re: year of HP ratings change. prop VS. crank

    inline 6s were around 81-82, v6s about 83-84

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    • #3
      Re: year of HP ratings change. prop VS. crank

      1985 was the first year all outboards had to meet propshaft specs.
      The only Roar you hear when running a 'Rude is the Roar of finely-tuned excuses in your wake

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      • #4
        Re: year of HP ratings change. prop VS. crank

        thanks much

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        • #5
          Re: year of HP ratings change. prop VS. crank

          How great is the difference between a propshaft hp rating and a crankshaft rating? Are we talking around 10%? Were some engines rated at the propshaft before it was mandated? Also "back in the day" were hp ratings certified, or did manufactures just slap stickers on the cowling as they saw fit.I notice that around 1984 OMC changed all the 35s to 30s......

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          • #6
            Re: year of HP ratings change. prop VS. crank

            well the hp ratings only have to be within 10 % of advertised. so that 250 yamaha you have could really be a 225 with a new cowl hood...i know old mercs used to be OVER powered.yes. when the motor is crankshaft rated, you usually lose around 10 5 by the time it gets to the prop. so if you have a 1982 100 horse and a 1986 100 horse, same brand, the 1986 will be more powerfull, not a lot, but if YOU dont want that extra 10 horsepower, let me have them

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            • #7
              Re: year of HP ratings change. prop VS. crank

              The Yamaha's were propshaft rated several years earlier than 85. Not sure of the other japanese manuf's.

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              • #8
                Re: year of HP ratings change. prop VS. crank

                ICOMIA Standard 28-83 was developed in 1983 (thus the -83 signification of the standard).The standard was developed because of the inconsistencies between some manufacturers rating their outboards at the prop and some at the crank.The hp losses due to prop ratings are minimal. 2-3%, maybe 5% at most. 10-15% is unreasonable as there is only one gear reduction and only a few bearings. You're simply not going to lose 20-25 hp to the prop on a 200 hp outboard.

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                • #9
                  Re: year of HP ratings change. prop VS. crank

                  1976-1983 200HP V6's(J/E), Only put out about 165 at the prop but were rated 200. This engine, with a few up-grades, became the 175 and a slot filled with the 185. With no up-grades, they were re-rated to 150...
                  The only Roar you hear when running a 'Rude is the Roar of finely-tuned excuses in your wake

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                  • #10
                    Re: year of HP ratings change. prop VS. crank

                    Forktail,remember the Icomia standard requires first a suggested WOT range , and then max HP rated in the mid of this range.

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                    • #11
                      Re: year of HP ratings change. prop VS. crank

                      Good point. But the rating is still based on WOT, whether it's WOT at 5000 rpm or WOT at 6000 rpm.The highest power within that WOT range can not exceed the declared power by more than 6% (section 6.2). Otherwise, it must be dual rated. Remember, the declared power will be at the mid point of the rpm range.So if you're rating your outboard at 200 HP with an operating range of 5000-6000 rpm, it can only produce 212 at 6000 rpm. Not 220 as the 10% corrected power would lead one to believe.

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                      • #12
                        My Honda 1984 Honda BF100 10 HP became the Honda 8 HP. It was down right painful being passed by Newer 9.9 Evinrudes back then.
                        In 1993 Evinrude (9.9 and 15hp ) increased their displacement 19% to 256cc to make 15HP at the Propeller shaft.
                        My math shows close to 20% difference.

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                        • #13
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                          Originally posted by sdanville View Post
                          My Honda 1984 Honda BF100 10 HP became the Honda 8 HP. It was down right painful being passed by Newer 9.9 Evinrudes back then.......
                          Please dont post to old inactive topics

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                          Money spent @ Boat Restoration should be measured in Smiles & Pride SHOP IBOATS-BOAT SPECS-FORUM HELP-REPAIR/RESTO

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