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  1. #1
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    1998 300 ProMax powerhead on 1996 250 EFI midsection?

    So will a 1998 300 ProMax powerhead bolt onto a 1996 250 EFI midsection and reuse lower unit, driveshaft and shifter shaft?

  2. #2
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    Yes,better if you have the 300 tuner,or just grind and clean up the 250 slag and casting lines,you'll have to mess around with pee hole hoses as the 300 came with an alien and o/shore mid,i did the opposite a few years back,put a 250xb on my 300 chassis,nothing major,to be scared of,make sure you ream all the carbon deposits (3/8" holes) out, for the idle reliefs in the adapter plate
    Last edited by Varmint; 03-19-2019 at 05:43 PM.

  3. #3
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    Ok, thanks for the comment. I came across a good deal on a 300 ProMax powerhead/motor but its got a 20" shaft and I need 25". I also have a few 25" 250 EFI motors sitting around.

  4. #4
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    Quote Originally Posted by Tinbanger1979 View Post
    Ok, thanks for the comment. I came across a good deal on a 300 ProMax powerhead/motor but its got a 20" shaft and I need 25". I also have a few 25" 250 EFI motors sitting around.
    That will work. 300 pmax came as a 25" they just added a 5" spacer to the 20" stump

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    Ok, I didn't know about the factory spacer. So I can mount the factory 5" spacer on the 20" midsection and use the 25" driveshaft/shifter shaft and Torquemaster lower unit from one of my 250 EFI motors?

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    yes,you need the correct studs that bolt into the midsection,to bolt up the spacer and l/u,,the TM studs are shorter than the sportmaster studs on a 3l. but the spacer slides onto the studs,they are M12 size and mercury still sells them. I have a buddy in Ga.,that may still have a 5" spacer. I may have the studs here somewhere,but they came out of a saltwater motor,best to get new ones.
    Last edited by Varmint; 03-21-2019 at 07:10 AM.

  7. #7
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    I have a 25” 1 piece triple ram mid I’ll trade for your 20”

  8. #8
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    I think he has a couple standard efi/opti 25" sections,the spacer is for his 300pm o/shore trunk
    Quote Originally Posted by hondatech View Post
    I have a 25” 1 piece triple ram mid I’ll trade for your 20”

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    Quote Originally Posted by Varmint View Post
    I think he has a couple standard efi/opti 25" sections,the spacer is for his 300pm o/shore trunk
    This is what I have.

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