VW Audi 1.9 TDI marinization

Discussion in 'DIY Marinizing' started by roedel, Mar 11, 2015.

  1. roedel
    Joined: May 2013
    Posts: 16
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    Location: CA

    roedel Junior Member

    I am working on a Marinization set to connect a VW TDI engine with an Mercruiser outdrive since a couple of years now, my target was to cut no corners, no matter how long that takes... well i never assumed it could take years....

    I have been posting about my project in another thread within this forum:


    I posted the whole project almost from the beginning in a forum specialized for TDI engines, if you are interested in all staged of my project please check here:


    Since i just finished the design of the coupler element between engine and Mercruiser out-drive i decided to open a new thread in this forum due to the fact that the coupler is very Boat specific.

    So here we go:

    Finished the new coupler this week. Since the Mercruiser drive shaft is firmly connected to the Gimbal housing and the gimbal housing is firmly attached to the Boat, the coupler needs to compensate all engine vibration and movements = Misalignment.

    The original Mercruiser design is not suitable to cope with the dynamics of a Diesel, only a few cm of rubber are available to isolate vibration.
    This is especially true since i plan to place the engine on silicon filled engine mounts, thus there will be a lot of movement.

    Here the original Mercruiser design:


    I decided to go for the "hardy disc" solution or flexible coupling, also used on many automotive drive shafts.

    Here an extract from the industrial coupling supplier Centa:

    "Based on a highly elastic rubber element subject only to compressive stress. Extremely high-performing design with high torsional elasticity. Dampens torsional vibrations and shocks and compensates considerable axial, radial and angular misalignments. Electrically insulating and thermally resistant in silicon design. For rupture-proof and backlash-free transmission of high torques. "

    So i purchased an industrial "flexible coupling" in the right range and firmness and had a sleeve machined in the right size.

    Only thing missing was the inside splines matching the Mercruiser shaft.
    So we measure the old coupler under the Microscope and drafted a CAD drawing based on that layout.


    Then had the splines cut by highly precise wire EDM.

    The part turned out perfectly, shaft fits into the sleeve with just the right amount of friction and play.



    I am ready now to finish the silicon rubber mounts, will test the boat in the next weeks with these new components under full throttle. I will run the test with the mechanical injection pump at the moment, will monitor Exhaust temperatures and test a water injection system to see how that helps.

    I have another engines prepared on a test stand, this one is my next generation with electronic pump. The test stand has a DYNO break so i will be able to test the engine performance.
    So far i have the first ECU tune finished and a complete new harness finished.
    Removed the EGR system and the MAF sensor to keep it as simple as possible.

    Next step will be to tune the thing for max performance, ideal for marine use.


    Stay tuned for updates
  2. roedel
    Joined: May 2013
    Posts: 16
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: CA

    roedel Junior Member

    Tested the TDi engine with mechanical injection successful. The little four banger could push the 25foot boat to plane with five people on board. We reached 22mph.
    Had water meth injected to keep EGTs under control and for about 30hp extra power. The boat planes without water methanol at around 19mph.
    Not bad for a first mockup trial.


    Only disadvantage i noticed with the mechanical injection is the during slow speed in the no wake zone, the engine vibrates more under mechanical injection compared to a electronically managed unit.

    Will do more testing and post updates.
    Last edited by a moderator: Apr 14, 2015
  3. roedel
    Joined: May 2013
    Posts: 16
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    Location: CA

    roedel Junior Member

  4. ben2go
    Joined: Jul 2008
    Posts: 187
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    Location: Upstate, South Carolina,USA

    ben2go Boat Builder Wanna Be

    I think a lot could be gained from gearing and prop selection.I'm not good with those.
  5. roedel
    Joined: May 2013
    Posts: 16
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: CA

    roedel Junior Member

    Hi Ben2go, i tried different props, made no big difference in low Rpm smoothness.

    The prop that performed best was the one that originally came with the V8.
    For low rpm smoothness electronic VE pump is the way to go.
    If the boat is mainly used at higher than wake speed mechanical pump is fine.

  6. MihaS
    Joined: Jan 2011
    Posts: 45
    Likes: 2, Points: 8, Legacy Rep: 29
    Location: Adriatic

    MihaS Junior Member

    roedel thanks for sharing with us your project.

    I was also in marinising project and engine works fine.

    Sound and power of 3.0 tdi engine is very usefull in boat.

    I also make about 120h and new buyer makes 90h and there are no any troubles with electronic or other parts.

    Now i have 4 new engines, not VW. Which i start to marinise. I have almoust finish the project.

    I make Laser cutted plate that goes to engine block and to original mercruiser bellhousing.

    i make wet exhaust manifold with expansion area on top. Also in manifold is installed water heat exchanger. Which i make from CuNi tubes.

    I found a problem with marinising car engines,because engines are not new and parts for overhouling are expensive.

    Now I found engines wich are in line six cylinder, 3800ccm, and have 560nM of torqe at 2500rpm.

    best regards

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