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Volvo Penta 305 swap to Mercruiser 350 MAG (MPI)

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Old 02-10-2008, 07:28 AM
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Default Volvo Penta 305 swap to Mercruiser 350 MAG (MPI)

I am buying a complete take out Mercruiser 350 MAG (MPI) from somebody that re-powered a cruiser and plan on freshening it up and swapping with my current 5.0 Volvo Penta (carb). 2st off, am I loco to put a Mercruiser in a VP boat? The price is right and I know the basic engines are identical so I think I am not too loco. Not sure what it has for bell housings etc., I pick it up today and will know more then. The guy did say it had a crack on the intake manifold, not sure what is about. Will post pics and more info later.
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Old 02-10-2008, 08:21 AM
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If the basic blocks and heads are the same Generation just freshen up the Merc long block and swap the Volvo accessories on to the new engine. If the Merc intake is cracked you will need to pick up a MPI manifold off of here or Ebay and you will be good to go.

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Old 02-10-2008, 08:52 AM
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You scare me when you mention bell housings.

Are you just swapping the block? Or are you going all the way back? If you are swapping the block, why would you think about bell housing (and transom assy)?

I would think that your "conversion" would meet at the coupler on the aft side of the block. Bolt on volvo coupler to meet the Volvo drive. Of course you need to pull the drive to get the spline out of the coupler. (You would have pulled it to release the old block anyway.)

If you are doing the whole drive and everything, you have a transom problem. The volvo transom assy and cutout is a match for OMC ironically, but not merc.

Note: people with OMC cobras can swap to Volvo DPX without any change of cut-out in transom.

If you are just swapping the block, it really hasn't become a merc. It's a "new" GM part. Still a volvo, just a repowered volvo.
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Old 02-10-2008, 12:35 PM
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If you are doing the whole drive and everything, you have a transom problem. The volvo transom assy and cutout is a match for OMC ironically, but not merc.
If you decide to replace the Volvo drive and transom assembly etc. then you can buy a Mercruiser transom adaptor kit.
But if your Volvo drive and transom assembly is in good condition then I suggest that you keep it.
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Old 02-10-2008, 04:15 PM
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Sorry, My post was not too clear. I just have the motor, ends at the flywheel. No starter or bell housing. I plan on keeping my old VP stuff , it is SX stuff and in great shape. SO I think it should be as easy as a flywheel (MPI had top mounted starter) and putting on my VP bell housing. Can they scan the ECU to see the hours? 1st thing is get a starter rigged up and see what the compression #s are but I was thinking since the intake is off, might as well pulls heads and have a look-see. They cut the main harness plug off (repowered original cruiser with diesels) so I gotta find a harness too.
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Old 02-11-2008, 06:12 AM
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I know that you are moving to a larger cylinder size... but not much. I keep wondering why you can use all of your volvo stuff, including harness, intake, ignition system and doing the equivalent of a long block swap out.
Not enough air/spark?
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Old 02-11-2008, 07:07 AM
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I guess from a work stand point the long block only swap would be easiest, for sure, then I could use all my VP stuff and drop in. I would really like to add the MPI though as compared to the current 4 barrel Holley.

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I know that you are moving to a larger cylinder size... but not much. I keep wondering why you can use all of your volvo stuff, including harness, intake, ignition system and doing the equivalent of a long block swap out.
Not enough air/spark?
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Old 02-11-2008, 08:29 AM
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Gotcha.
That's what I figured.

I see that you are in salt water, so you probably don't want an aluminum intake manifold, but when I was doing a non-stock repower of a 350 merc once I used the Mallory Marine Magnetic breakerless ignition, an Edelbrock Performer intake manifold and a quadrajet with very good results.
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Old 02-11-2008, 08:35 PM
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I have not ripped it apart yet but it sure looks like the OEM manifold is aluminum...am I smoking crack? I agree, I am in salt and no closed cooling so cast iron is what I am after.
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Old 02-12-2008, 11:01 AM
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Suddenly I am wondering why the intake is cracked, and if it was run while it was cracked, and if there are other problems brewing in the cylinders because of a cracked intake.

Is it cracked in such a way as to allow water into the mix?
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