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DIY - Duramax Marinisation

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Old 03-20-2016, 06:59 PM
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Default DIY - Duramax Marinisation

Being between personal builds, I've been helping out on a couple new 6.6L Duramax marinisation projects over the winter. Since I've logged the most hours on the water and under the hatch with this platform, figured some of you might be interested in seeing what's actually involved these swaps.

The first build is a 33' Sonic [deep V cruiser] with a single700hp twin turbo Duramax, mated to 6spd Allison trans, an a ASD #8 drive. https://youtu.be/eGwc9gZMmx0
That one is a true DIY boaters build whose previous works include a T56 turbine powered cat. Which turns out had an easier learning curve than this diesel build. After a small catastrophic engine failure, the lessons learned here will ultimately make this a "how to" example for anyone looking to do a similar swap in the future.

The second boat is a larger center console fishing boat with two mildly modified [stock bottom end] 2014 LML's connected to Merc #6 drives. This one is more of a classic BBC to Duramax diesel engine swap. It includes a more "plug N play" approach with a custom engine harness and drive by wire helm. The way I'd like to assemble a simple swap kit to make this a couple weekend project, rather than a full on re-rigging job.

Campaigning my own one-off marinisation for several years, the question ask the most was; How much does it cost to convert a Duramax to marine use. Truth of that, to date, far more than buying a brand new 6.6L Duramax from the GM factory... Hence the main reason you don't see many of them out there. Less than 10 [non-military] builds that I know of. And yes today you can buy a fully marinised 500hp Duramax for a little over 30k, and drop another 30+ into a matching outdrive to handle it. But for that same money you can build a healthy BBC and buy a lot of fuel to feed it...

So I started this thread to explain how these swaps can be done right, and on a budget. Hopefully simplifying this reliable diesel platform that out performs the larger cubes BBC in all areas, for less than that new crate motor. To do this we'll take to look at each part of the marinisation process required to keep this swap clean, reliable, and affordable.

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Old 03-20-2016, 08:12 PM
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good stuff,thanks for posting.how about posting more pictures.
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Old 03-20-2016, 11:15 PM
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Ok lets start with the easy parts for a BBC swap. Things you won't need to buy..

Luckily the typical light duty 2500-3500 series Duramax equipped trucks and a BBC share bell a housing bolt patterns. So your std Bravo rear mount and HP dampener will bolt right up.

[ATTACH=CONFIG]552733[/ATTACH] [ATTACH=CONFIG]552737[/ATTACH]

For those looking to run a larger marine trans like ZF, the Duramax uses a adapter plate between the block and transmission. This means you can switch from GM to SAE bolt pattern bell housings by boneyard or eBay shopping. These SAE 30 adapters were used in medium duty 4500 series and and up.

[ATTACH=CONFIG]552735[/ATTACH]

Flywheel options, are just that. All the builds I been involved with so far have used a custom $1200 billet flywheel drilled to match the Merc rubber dampener or velvet drive dampener. I do know of a boat running a factory flex plate without issue. But because of the engine torque and spinning inertia, I would likely stick with something heavier. But in the $600 range.. More on this one later.

[ATTACH=CONFIG]552736[/ATTACH]

That pretty much covers the rear of the engine. Now onto the front of our engines.

Once again, no big purchases required. Only a custom Merc seawater pump bracket and new serpentine belt is required.

[ATTACH=CONFIG]552734[/ATTACH]

The factory alternator and power steering pump will work just fine. Because it's diesel, no special marine starter or alternator is required to be USCG leagal for these swaps. But there is an actual part number for a marine starter I found...

You can also leave or remove the AC compressor without issue. In my first post, see pic of my engine, notice the ECM is mounted where the AC pump would typically be found. However if I was converting a boat with a cabin, I'd keep one AC compressor connected and put that puppy to good use. Factory water pump on the Duramax is gear driven off the crank, so belt routing options are wide open. There is several idler positions that will let you delete everything keeping just alternator and seawater pump if no PS pump is required. Typical seawater pump location is shown in pic the below.

[ATTACH=CONFIG]552738[/ATTACH]

More to come.
Attached Thumbnails
DIY - Duramax Marinisation-engine-2_small.jpg   DIY - Duramax Marinisation-bracket1.jpg   DIY - Duramax Marinisation-010913th00-071.jpg  

DIY - Duramax Marinisation-marinebilletflywheel.jpg   DIY - Duramax Marinisation-velvet_bell.jpg   DIY - Duramax Marinisation-belt_routing.jpg  


Last edited by kidturbo; 03-21-2016 at 12:00 AM.
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Old 03-21-2016, 03:48 AM
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Very interesting info, I'm subscribed........
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Old 03-21-2016, 10:11 AM
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Good stuff man, keep it coming
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Old 03-21-2016, 04:33 PM
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Couple other pieces that can be used off the gas engine depends on your current rigging setup. The front motor mounts on my setup were factory Merc BBC mounts. Two of the block bolt holes lined up perfectly, while a third was re-drilled. My stringer width required a piece of angle on each side to center up the engine. Believe that was same as the factory though.

[ATTACH=CONFIG]552757[/ATTACH]

PPE sells a Duramx set with adjustable stringer mounts included But access to some basic machining tools can save ya $500.

[ATTACH=CONFIG]552758[/ATTACH]

My buddy Dave designed his own mounts to match his stringers [below]. While the twin engine setup is going with an offshore style mounting which I'll try to get a pic of when they get dropped in. The Duramax block has a couple different mounting patterns on each side, so it's really up to what fits your engine bay.

[ATTACH=CONFIG]552759[/ATTACH]
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DIY - Duramax Marinisation-photo4.jpg   DIY - Duramax Marinisation-marinestationaryenginemountkit_v1.jpg   DIY - Duramax Marinisation-imagejpeg_0_5.jpg  

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Old 03-21-2016, 04:57 PM
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very cool info !!!
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Old 03-21-2016, 09:34 PM
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Received these custom DIY motor mount pics to share.

[ATTACH=CONFIG]552769[/ATTACH][ATTACH=CONFIG]552770[/ATTACH]

[ATTACH=CONFIG]552767[/ATTACH][ATTACH=CONFIG]552768[/ATTACH]

As you can see, getting the Duramax bolted up in a boat is probably the easiest part of this swap. There is two factory oil pan options, regular 10qrt and medium duty 12qrt designs. The 10qrt setup ends up holding about 12 with remote filter and cooler. And for those needing a lower CG, or looking to do serous off shore running, a dry sump pan is also available from multiple suppliers.
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DIY - Duramax Marinisation-fullsizerender2.jpg   DIY - Duramax Marinisation-imagejpeg_0_7.jpg   DIY - Duramax Marinisation-fullsizerender1_1.jpg  

DIY - Duramax Marinisation-imagejpeg_0_6.jpg  
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Old 03-21-2016, 10:20 PM
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Ken here's a template for bolting a two or three stage BBC pump to the front of the block. When you get time to talk about the control and tuning please explain why it's important to start with the right series engines.
I started with LML's not knowing their ECM's are too complicated for a stand alone harness unlike the earlier series Duramax's. The fix was to swap out the fuel system for LBZ
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Old 03-21-2016, 10:39 PM
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Killer!

Thanks for the taking the time to share your expertise.

Love the marinised diesels.
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