High Pressure Turbo Diesel

Discussion in 'DIY Marinizing' started by graywolf, Dec 15, 2014.

  1. graywolf
    Joined: Dec 2014
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    graywolf Junior Member

    There are several newer small auto turbo diesel engines running high boost pressure, 15psi or more. The only thing I see wrong with them is that the old school marinizing methods do not seem right.

    The turbine uses the energy from the engine exhaust to drive the supercharger. So cooling the exhaust manifold seems to be contrary to what we would want to do. It seems like the exhaust should be heat wrapped, and maybe the turbine too, to keep the exhaust flow moving as fast as possible while protecting the engine compartment from excess heat. Although water cooling the turbine might turn out to be needed (I have seen the things glowing on racing --gasoline-- engines), but am hoping wrapping it would do. and since the most expensive marinizing part is the water cooled exhaust header, it should be cheaper doing it that way.

    Then there is the intercooler, it would seem like a good idea to use raw water cooling on it to get the maximum air density. So raw water to the intercooler, to the heat exchanger, to the exhaust pipe (???).

    I see good running engines with a warranty for $1000 to $1500 (also without a warranty for 2-3 times that much, to be sure). Maybe the needed mods for another $1000 ($2000 with that pesky header). So a 100hp-120hp engine for fairly cheap. That seems fine for a 20-22 foot wood sea skiff style boat.

    Am I missing something obvious here? Does anyone have any idea what a water cooled turbine goes for, if that would be necessary?
     
  2. CDK
    Joined: Aug 2007
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    CDK retired engineer

    You overestimate the effects of a water cooled manifold on exhaust gas temperature.
    In road vehicles the airstream keeps the manifold temperature down, in marine applications water does the same. Yes, with a heat wrapped manifold the volume of the exhaust gases would be somewhat larger, but it shortens the life expectancy of both the manifold and the turbine.
    Even with a water cooled manifold there is enough boost pressure to open the waste gate. I marinized VW turbo diesels and was surprised to find quite high turbine temperatures, comparable to those in road vehicles. Only at the turbine output where raw water is injected in the exhaust stream the temperature drops sharply so rubber hoses can be used.
     
  3. FAST FRED
    Joined: Oct 2002
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    FAST FRED Senior Member

    > So a 100hp-120hp engine for fairly cheap. That seems fine for a 20-22 foot wood sea skiff style boat.<

    ONLY if the full engine output will be used for very short periods of time , like climbing up on the plane , then 50%+ pullback.

    Car engines are not built to work at full output for very long .BIG Truck engines are heavier for a reason ,full throttle for hours if required . not just 0-60 in 4 seconds.

    Divide the car engines cubic inch displacement by 3 , and use that as your cruise HP .
     
  4. graywolf
    Joined: Dec 2014
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    graywolf Junior Member

    Hate to say it, but you do not seem to be up on modern engines, or even older ones. For example the 2.0 liter 53hp @ 4500 rpm (5000rpm redline) Mazda RF diesel in my '86 Ford Escort had no problem climbing mountains at 4000 rpm for an hour at a time. Of course it was probably only producing 15hp or so up there at 11,500 feet in the pass (one time in Idaho).

    The glowing turbo I mentioned was in a friends Mazda race car. Admittedly it blew up after about 15-20 minutes, but then it was putting better than 400hp into the chassis dynamometer when it was being tuned, that from a 2 liter engine. At 200-250hp it would have run forever. And diesels are even stronger to start with than that gasoline engine.

    The diesels we are talking about are rated 150-225hp in the cars (between 2.0 and 2.4 liters), so running them at 120hp is already quite a derating.

    The boat in question ran real well with a 120hp Chrysler flathead six in it. The set up like I am talking about would drop the trailer weight of the boat by about 500 pounds down to 2,000 pounds or so (That Chrysler engine and transmission weighted about 1400 pounds).
     
  5. graywolf
    Joined: Dec 2014
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    graywolf Junior Member

    CDK, I had read your posts on the VW's with great interest. Unfortunately, it sounded like you needed another 100hp to get that boat up on the plane.

    My main reason for not wanting to water cool the manifold is the $1000+ dollar price for the things. I guess one-offs could be fabricated from wrought iron pipe (gas pipe) as it is very rust resistant. Now that you mention it, I would think that since the turbocharger would be boosting all the time you would have pretty high temperatures. It makes me wonder if a mechanically driven supercharger would not work just as well in a boat? Might actually be more reliable too.
     

  6. FAST FRED
    Joined: Oct 2002
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    FAST FRED Senior Member

    The boat in question ran real well with a 120hp Chrysler flathead six in it.

    Gas engines are usually operated at the 50% load , so IF 60 hp is required that engine would be fine.

    >The diesels we are talking about are rated 150-225hp in the cars (between 2.0 and 2.4 liters), so running them at 120hp is already quite a derating.

    For about $100 an EGT meter can be had , I would use it to observe how much power can be used before meltdown.

    High output engines are not new , the hassle is service life,

    A DD 6-71 at 500-600 hp will have a service life of 500 to 1000 hours ,

    Un hot rodded it will run 25,000-30,000 as a prime gen set at 120hp.

    Most pleasure boats or light work boats will chose 180HP at probably 10,000-15,000 hours.

    Your choice, but for 60-120 hp simply lagging the turbo should hold the heat in the engine space to managable.
     
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