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  1. #1
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    25 inch mid section vs a 20 inch mid section

    A novice question. What are the pros and cons of using a 25 inch mid over a 20 inch mid I run a 21 Action Marine with a 25 inch and my brother in law runs a 20 inch. I donít really see a difference in performance. Iím running a 2.4 200 and he is running a 225 Optimax. People have told me that I would easily gain 3-4 mph going to a 20 inch mid section. I just donít see it. Our boats run neck and neck. Will the 20 inch lower really improve performance? If so why? Drag reduction? Resistance
    Thanks in advance
    Tom

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  3. #2
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    The size of the mid is usually a product of the design of the boat. The lower the powerhead the lower the cog. Helps with the handling. Shorter mid is lighter. Most important is the relationship tween the bottom of boat and prop.

    Rock
    Team Junk

    No sparkling wiggles in here, only dump truck grinches.

    "Screamin Heathen"

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  5. #3
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    Rock answered it on point. Different boats have different sized transom heights and the difference is to get the prop into to the sweet spot for a particular boat. The other thing I've noticed is racing setups almost always have a 20" inch or 15" probably to reduce weight (or boat design) except for the 25" offshore mid which is pretty rare.
    I'm not sure if a racing motor like a 280 can go onto a standard 25" mid and not cause issues with the increased torque or not. If anyone has information on that it would be cool to know if I could ever throw a higher hp 2.5l powerhead on my 25" standard mid.

  6. #4
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    Quote Originally Posted by Fishinmymission View Post
    Rock answered it on point. Different boats have different sized transom heights and the difference is to get the prop into to the sweet spot for a particular boat. The other thing I've noticed is racing setups almost always have a 20" inch or 15" probably to reduce weight (or boat design) except for the 25" offshore mid which is pretty rare.
    I'm not sure if a racing motor like a 280 can go onto a standard 25" mid and not cause issues with the increased torque or not. If anyone has information on that it would be cool to know if I could ever throw a higher hp 2.5l powerhead on my 25" standard mid.
    I would think you could , worst case scenario mite need harder driveshaft

  7. #5
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    Quote Originally Posted by Fishinmymission View Post
    Rock answered it on point. Different boats have different sized transom heights and the difference is to get the prop into to the sweet spot for a particular boat. The other thing I've noticed is racing setups almost always have a 20" inch or 15" probably to reduce weight (or boat design) except for the 25" offshore mid which is pretty rare.
    I'm not sure if a racing motor like a 280 can go onto a standard 25" mid and not cause issues with the increased torque or not. If anyone has information on that it would be cool to know if I could ever throw a higher hp 2.5l powerhead on my 25" standard mid.
    Quote Originally Posted by Merc 2.5 View Post
    I would think you could , worst case scenario mite need harder driveshaft
    The driveshaft is the limiting factor. The longer the shaft absorbs more power and that power is absorbed into heat and vibration. I'm not sure what the RPM limit is on a 25" shaft but I wouldn't suggest running a lot of RPM through one. I would guess 6,000-6,500 is about all you would want to put through a 25" shaft. I've never run one so that's just a guess...

  8. #6
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    Lowers can always be swapped. I'm wondering why the offshore 25" is the only setup for racing 2.5L. I wonder if the housing may distort with the torque(prop to transom moment) of 5 more inches which is why the 25" standard is only offered on up to the 200 EFI and at only 15" and 20" on the higher hp racing motors.

    Maybe the offshore is more rigid to prevent distortion which could equate to less misalignment on the longer 25" mids when running at full load?
    Last edited by Fishinmymission; 01-30-2019 at 06:33 PM.

  9. #7
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    Quote Originally Posted by maineidyl View Post
    A novice question. What are the pros and cons of using a 25 inch mid over a 20 inch mid I run a 21 Action Marine with a 25 inch and my brother in law runs a 20 inch. I don’t really see a difference in performance. I’m running a 2.4 200 and he is running a 225 Optimax. People have told me that I would easily gain 3-4 mph going to a 20 inch mid section. I just don’t see it. Our boats run neck and neck. Will the 20 inch lower really improve performance? If so why? Drag reduction? Resistance
    Thanks in advance
    Tom
    Hi Tom, read the bold! COG or CG = Center Of Gravity...

    Quote Originally Posted by rock View Post
    The size of the mid is usually a product of the design of the boat. The lower the powerhead the lower the cog. Helps with the handling. Shorter mid is lighter. Most important is the relationship tween the bottom of boat and prop.

    Rock
    Leverage for one thing. A 20" mid is more stable. 15" even better. Some boats need a 20-25" to keep the power head out of the water. There is no other reason.

    As Rock said, depth of the lower in relation to the bottom is the key. Sounds like it is close if you are running with your BIL.

    "If it ain't broke, don't fix it!"
    I may have been born at night, but it wasn't last night.

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  11. #8
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    Looking at two motors. Ones a 25 inch 250xs without a spacer and one is a 25 inch 250xs with a spacer and coupler. Have heard from some that the 25 will cause the boat to handle bad. I just can’t grasp how. If the CG is higher and it affects handling are we speaking of turning etc. or chine walking?some have said it will only show when running over 70 which doesn’t concern me. Not planning on spending a lot of time above those speeds.
    Any ideas?
    Tom

  12. #9
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    On boats with shorter transoms, if you raise a 25" motor high enough for optimal performance sometimes having the powerhead so high over the transom it upsets the balance of the boat. If the propshaft is too low in the water it causes adverse handling when you trim the engine up.

  13. #10
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    Mine will be on a 10 inch hydraulic jackplate.

  14. #11
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    Will be even worse with that setback. The more setback you have the higher the prop shaft should be in relation to the hull.

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