2000 Sundancer 240 5.0L seized! MAG 350 MPI upgrade??

Discussion in 'Gas Engines/Drives/Transmissions/Props' started by David Cibin, Mar 2, 2021.

  1. David Cibin

    David Cibin New Member

    Feb 9, 2021
    2000 Sundancer 240 DA, 2006 Larson 180 SEI, 2011 Ram 1500 5.7 Hemi
    Mercruiser 5.0l EFI Bravo II
    I'm looking to upgrade the engine as my mercruiser 305 is seized. Today I came across to a 1999(to confirm serial yet) mercruiser 350 MAG MPI. This 350 has the transmission attached to it. So I'd like to know if this would be a drop in situation after remove the trans or will it need any sort of modification? Or any other mod at all?
    I also found very nice deals, all of them 350 as well but all carbureted. But I'm not sure if I could reuse parts from my 305 EFI to swap to the 350.
    Last but not least, the 350 MAG has the closed cooling system, is good or not??

    btw I have the Bravo II


    Attached Files:

  2. Chip S

    Chip S Active Member

    Jun 17, 2019
    Bordentown, NJ
    1993 Sea Ray 200 Overnighter
    1993 Mercury 150 hp Black Max Outboard
    I'm pretty sure an inboard engine (with the transmission) is not a direct replacement for a sterndrive engine. I'm not sure if it can be modified to work. I'll defer to the mechanics on the forum regarding that.

    I had bad experiences with the 350 MAG (5.7 L) and would stay away from that engine. Mercruiser no longer sells it. Mercruiser now sells the 6.2 L as the 300 hp option. Lower horsepower 5.7 L engines are fine. I would just avoid the 350 MAG.

    A closed cooling system is good. If your old engine is not closed cooling, you may need to make some modifications to use it. I'll again defer to the mechanics on the forum about that.
  3. HawkX66

    HawkX66 Active Member

    Jul 27, 2020
    SE Virginia and Mass
    "Tread Knot"
    1997 Sea Ray Sundancer 290DA
    454 L29 Carb w/ Bravo III
    There was never a more versatile or reliable power built motor than the small block Chevy 350. Unless I'm missing something, all that you should have to do to make it work is remove the transmission and get a coupler assembly on it with pressure plate. Anything from your 305 should bolt on with no modifications necessary.
    The unknown is the condition of the motor as far as I can tell. Fresh Water Cooling is awesome as far as I'm concerned. Takes the salt water out of most of the issues except for exhaust.
  4. Lazy Daze

    Lazy Daze Well-Known Member TECHNICAL Contributor GOLD Sponsor

    Apr 21, 2009
    The 350MAG was one of Mercruiser's best selling and best performing engines for decades, for good reason - great engine. The reason it is no longer is made is simply because Merc is no longer using GM blocks and they are using their own designs. I've never done a swap from an inboard to stern drive, but off hand, I can't imagine why it wouldn't work - as noted, your engine coupler and other things should bolt right up. But maybe someone with more specific knowledge can add some info. Fresh water cooling is only a bonus to you - whether you continue to use it or not, is your choice.

    You'll probably need to up the pitch of your current prop. Just make sure you think this through, buying a used engine - a new or reman longblock smallblock can be found for a few thousand, tops.
  5. hughespat57

    hughespat57 Active Member

    Sep 25, 2016
    Rock Hill, SC
    300 Sundancer 1994, trailered tri-axle LoadRite roller
    Mercruiser 5.7 260HP Alpha One Gen II, twin
    Some good, some bad, some ugly...

    Yes they are both Small block Chevy engines
    Yes MOST parts will be interchangeable
    Yes fresh water cooling is a good thing, the block should have no internal corrosion.
    If half system the manifolds are still saltwater cooled
    If a full system the manifold is fresh water but riser elbow is still salt water
    Cant till for sure from that photo angle if 1/2 or full fresh water, but looks like 1/2

    You need to lose the transmission, bell housing, starter, flywheel adapter,
    You need the same from the current engine.
    Flywheel could be an issue, may need that to, if it will bolt up, (probably will)

    The starter has to go because it is tucked under the manifold on a stern drive.

    There is horsepower and there is displacement
    You need to know for sure, what your current engine is, there were many 5.0L options in different HP
    Higher horse power may be a 1.5 out drive gear ratio, the lower HP had a 1.65 ratio (to low for a 5.7/350HP)
    You have a BRAVO II correct?

    The 350MAG is 350HP from 5.7L (350CI)
    as compared to say my 5.7L(350CI) @ only 260HP
    typical 5.0 that years was 220-240

    So do more research on what you have and what might have to change

    Sea Ray prop chart shows all BII had 2.20:1 ratio 5.0 or 5.7
    prop changes from 5.0/220HP-17 3/4x21 to 5.7EFI/260HP - 16 1/4x25
    Last edited: Mar 2, 2021
    Soulshine likes this.

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