Thread: Cowling Mod

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  1. #1
    Member terry5357's Avatar
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    Cowling Mod

    I'm curious how modding the cowling which allows more air into the cowling can give big enough horsepower gains to push a boat 1 1/2 mph faster. To me seems like the same thing as flipping an air cleaner cover over or removing it and expecting a 5 % horsepower gain, doesn't make sense. Again I'm no outboard motor gear head.
    1996 ProGator 200V
    1998 Mercury 225 EFI
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  2. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #2
    Are we talking about your 225 EFI (specifically)?

    In order for the above description to be accurate, the engine would have been running poorly in the first place (richer than intended/designed, such as might be the case with injectors in dire need of service/calibration).


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
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    #3
    Quote Originally Posted by terry5357 View Post
    I'm curious how modding the cowling which allows more air into the cowling can give big enough horsepower gains to push a boat 1 1/2 mph faster. To me seems like the same thing as flipping an air cleaner cover over or removing it and expecting a 5 % horsepower gain, doesn't make sense. Again I'm no outboard motor gear head.
    Unlike most cars, there is restricted air flow in most outboards. The cowling mods get rid of the restrictions. Most EFI motors compensate and correct mixture rate. Most carb motors are way too rich so it not only improves air flow, but improves mixture ratio. I don't think DFI motors compensate, so I would not try it on a DFI motor.

  4. Member terry5357's Avatar
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    #4
    ^^^^ Thank you Sit, hopefully you can see my confusion as to why that would help. I can definitely see how the motor could be starving for air with the cowling as enclosed as it is.
    1996 ProGator 200V
    1998 Mercury 225 EFI
    New Carpet
    Seastar Pro Hyd Steering
    Minn Kota Ultrex

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    #5
    When I did my old 99 225efi I didn't see any top end gains but I did see performance gains, as well as when I went to higher elevations. Ran much better and didn't loose as much top end as previous.

  6. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
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    #6
    Quote Originally Posted by John Jackson View Post
    Unlike most cars, there is restricted air flow in most outboards. The cowling mods get rid of the restrictions. Most EFI motors compensate and correct mixture rate. Most carb motors are way too rich so it not only improves air flow, but improves mixture ratio. I don't think DFI motors compensate, so I would not try it on a DFI motor.
    In our Mercury engines- BOTH the EFI and DFI/Optimax engines are "Speed/Density" systems. NEITHER of them have the ability to realize or compensate for any changes in airflow.

    Most of the EFI engines (especially the earlier ones) were pretty fat/rich, so they ended up a bit more "forgiving" when it comes to this topic.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
    Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor