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Tohatsu 9.8HP 4 Stroke to 15 HP Upgrade Not Quite Right?

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  • Tohatsu 9.8HP 4 Stroke to 15 HP Upgrade Not Quite Right?

    I've been reading the forums on this topic but still have a couple questions. I have 2010 tohatsu MFS9.8A3EFS model and am interested in the HP increase modification I've read about. I've read that simply need to replace carburator to 15 HP model and that's all. But when I look at Tohatsu website the specifications for the 9.8 and 15 HP are quite different.

    For example:
    9.8 HP
    -209 cc displacement
    -82 lbs

    15 HP
    -351 cc displacement
    -114 lbs

    I don't understand how the 9.8 can develop the 15HP with 140 fewer cc displacement? Also the weight difference is a concern. The 15 HP carb isn't going to weigh an extra 30 lbs, so that means that there are addtional differences like shafts, gears and other components that would need to be bulked up on the 15 HP model? It just doesn't add up. Thanks in advance for all the information on the forums, it is a great resource!


  • #2
    Re: Tohatsu 9.8HP 4 Stroke to 15 HP Upgrade Not Quite Right?

    From my understanding you cannot make the 9.8 into a 15, you are talking about two completely different engines whether two or four stroke. I think people are seeing 9.9 and 9.8 and thinking they are the same engine, they are not.

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    • #3
      Re: Tohatsu 9.8HP 4 Stroke to 15 HP Upgrade Not Quite Right?

      Correct. Some (not all) 9.9's could be upgraded. The 9.8 is not a 9.9; It is already the "big brother" of the 8 hp motor; i. e. it has already been "upgraded".
      Paul
      Certified TLDI Technician
      Buffalo NY USA

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      • #4
        Re: Tohatsu 9.8HP 4 Stroke to 15 HP Upgrade Not Quite Right?

        Ah, very good. 9.9 vs 9.8, i'd never have thought they were different. good thing we have such knowledgeable people on the forum with lots of experience. thanks for saving me the carb swap!!

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