Aircooled manifold, water cooled exhaust?

Discussion in 'DIY Marinizing' started by DennisRB, Dec 10, 2016.

  1. FAST FRED
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    FAST FRED Senior Member

    "All engines have an optimum operating temp and keeping an auto engine at right temp in a boat is not difficult."

    The best of course is to forget the "conversion process" and use a dry stack exhaust with keel cooling.

    The std cooling water pump is fine for circulating water to the keel cooler , and for the cold weather sailors , no winterizing is needed every day when it will be 0F at the dock after a run.A built in flush keel cooler will get rid of grah for the fast 20K boats.

    With the dry exhaust run up a pipe the engine stink gone.

    With modest insulation the exhaust manifold will not place enough heat into the engine room that it can not be extracted..

    Sure its a bigger engine room blower , but considering the savings from not "converting" an engine , the cost is minor.

    Air coming out of the ER will require a duct work ,with noise insulation, to baffle the sound of the engine.

    Making it 10% bigger to assure low temps for the engine operation would cost very little.

    Just be sure to build a good hatch over the engine , so if you should wear it out , a trip to the wreckers and a few hours of work will cure it.

    The only expense that would be extra if the auto tranny is used would be for a thrust bearing on the prop shaft.
     
  2. tom kane
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    tom kane Senior Member

    aircooled maniofold, water cooled exhaust

    DennisRB..I am not saying exhausts of any sort have any relationship with the transmission, just that I would not run water inside my exhaust but would use raw water water if necessary through jacket hot spots on the exhaust.
    Dry exhausts for me.

    It would be a good idea take all the advantages of auto exhausts and future proof you boat by including the emission control systems and that is not compatible with internal water cooling the exhaust.

    Fast Fred seems to have it all right except worrying about the thrust bearing on the prop shaft which are cheap,necessary and easily incorporated.

    http://www.boatdesign.net/forums/at...ing-engine-compartment-nissan-remote-fuel.jpg
     

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    Last edited: Dec 12, 2016
  3. tom kane
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    tom kane Senior Member

    Last edited: Dec 16, 2016
  4. mcl
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    mcl Junior Member

    You can use a insulated exhaust manifold,use the original cast iron manifold,wrap it in insulation and build a box out of sheet stainles steel for example.You will however need a watercooled turbo,im talking about the centre portion with the bearings.The turbine housing can be air cooled as well and insulated as above.

    Problem is most turbos that come stock on a car diesel engine is way to small for the engine in marine configuration,the turbos are air/oil cooled.Running a turbo like this will get so hot that the oil that lubricates and cools the oil will start to burn and turn to carbon,and the turbos life will be very short.I have seen installations like this melting plastic several feets away.

    And automotive style exhaust in a boat will need some serious insulation and space.

    Im doing a marinazition myself with a ford 2.5 td engine.Due to budget reasons im also using a aircooled turbo of a bigger and more powerful mercedes car engine.The exhaust manifold is waterjacketed,turbine housing is isolated,the turbo is fed oil by a copper pipe which further cools the turbo oil before the turbo,it also has a bilge blower cooling the turbo centre housing with air.Fully syntethic motor oil also helps as it needs substantially higher temperatures to break down compared to its mineral counterparts
     
  5. DennisRB
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    DennisRB Senior Member

    The turbo watercooling is a non issue as its fed by a small hose from the coolant water.
     
  6. mcl
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    mcl Junior Member

    Thats a water cooled turbo,then there is no issue in just insulating and covering the manifold and turbine housing.I work on large ship diesels and thats how its done most of the time.The turbines are the size of a car engine,funnily enough they have their own lubrication system which has about 1.5 liter of lubricating oil.Not much considering the size.

    The engines has individual exhaust gas temperature measuring for each cylinder.The larms go off at 500C,most of the times high egt is caused by dirty airfilters or charge air leaks,meaning engine doesnt get enough air compared to the amount fuel injected.Could also be caused by leaking exhaust valves and a few other issues.It ould be neat to have the same measuring capabilities on a leisure boat engine,really helps to troubleshoot when you can build a baseline of values for different engine loads.
     
  7. mcl
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    mcl Junior Member

    Ive read your first post and there is no need to use a fan to funnel air to cool the manifold.Just wrap the hot parts with insulation/thermal tape and box it in with stainless.Manifolds and turbine housings dont get that hot on diesels if you are running it right=Enough boost and low egt.

    A simple way to think charge air pressure,injected fuel and egt goes something like this.You have your engine running a a certain speed and injecting a certain amount of fuel,with no boost pressure you have just enough air to burn all the fuel,there might be a bit black soot out the exhaust since all the fuel isnt being properly burnt and the egt are high due no excessive air.The engine is producing 100hp
    No you shut the wastegate and the turbo starts building up pressure,say youre now ramming twice the amount of air into the cylinder.The engine is still producing the same 100hp power since the same amount of fuel is injected,but there is no soot and the egt is alot lower.This is due to the thermal energy released by combustion now has to heat up twice the amount of air as before.
    Now you start injecting more fuel.Power and egt goes up,this is due to more thermal energy is being released and the ratio of air to burn the fuel gets smaller.

    A charge air cooler is also very important in marinizing a car engine.At work we have engines running at full chatter the boost pressure is 1.9 bars and the charge air temperature before the cooler is 110 degrees C,hotter than the boiling point of water in atmospheric conditions.Without a charge air cooler thats quite hot air your feeding to and already hot engine.

    Ive seen mercedes om606 engines in cars producing over 600hp out of a 3l diesel.You can bet that engine is injecting all the amount of fuel it can with boost pressures way over 2 bars and smoking like a chimney.It might work ok for intermittent power use,but do it continuously and I would be surprised if it could deliver even half of that continuosly without melting pistons.

    What im coming with this is car engines are designed for intermittent use,they are not designed to run at 100% load all the time.This is why its better to use a truck/van engine as a base engine as they are more designed for heavy pulling(trailers and such).
    Alot of marinizing projects start out by the users personal experience of the engine in light car use,its very reliable and you can easily chip it for more power.When in fact that engine can maybe run 2/3 of its car output in the marine environment before oil and egt temps start to skyrocket.

    Got a bit carried away but hopefully it helps people with their projects :)
     
  8. DennisRB
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    DennisRB Senior Member

    Hi thanks for the post. Im no stranger to turbocharging. I did my own project 6 cyl street drag car. I dove it everyday to work etc and it still done a 10.8 quarter mile and had over 600hp.

    For this project I wanted to use a non turbocharged gasoline engine say out of a Toyota Yaris or similar. The power would be much more than required for a sailboat aux so it would not be overloaded and new engines would be a few hundred dollars.
     
  9. mcl
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    mcl Junior Member

    I think it would work fine,although I would be cautious using non watercooled exhaust on gasoline engines.The exhaust gets alot hotter and is very hot even at idle with no load,also gasoline is very flammable compared to diesel.

    I dont know what kind of power you need to draw but seems that even the smallest car engines would be grossly underloaded.
     
  10. tom kane
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    tom kane Senior Member

    There is no need to worry about gasoline engines in boats if you have a remote fuel system.
    http://shareaproject.com/manageProject.php?p=9

    All your gas engine in boats problems solved.Carb or EFI. It`s just about how you design your boat.
     
  11. DennisRB
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    DennisRB Senior Member

    Tom. What do you mean about a remote fuel system? Seems all but the smallest outboards have remote fuel systems?
     
  12. gonzo
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    gonzo Senior Member

    There one way to cool down the manifold without a shroud. Wrap it tightly with copper pipe where you circulate water through. It could even use two layers. Then use a fiberglass wrap around it if you want more insulation.
     
  13. DennisRB
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    DennisRB Senior Member

    How about the use of an eductor / venturi reasonably close after the exhaust manifold to suck fresh air into the exhaust pipe? This would cool the exhaust gas down to reduce engine bay temps and probably reduce noise?
     
  14. FAST FRED
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    FAST FRED Senior Member

    Seems it could be much simpler.

    Laced on insulation on the exhaust would keep most, much , some of the heat from the engine room.

    Just so you don't get burned if you touch the exhaust .

    Simply install a BIG! engine room power vent system (the engine alt can make the power).

    Car electric cooling fans are DC powered and really powerful, so all that is needed is a 12x14 duct with some noise insulation for the engine to operate in cool enough air.

    KISS!
     

  15. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I think you're going about this from the wrong set of angles. I've had great success with cooling both air and liquid cooled engines of every size for years. Unlike a lot of places, Florida is an extreme environment for most engines, especially air cooled. Lowering these temperatures where appropriate and containing where appropriate is key and going to make any engine live a lot longer. The trick is understanding what you need and for an exhaust you need to contain the heat for efficiency, but also dampen noise and radiant heat. The dampening part is pretty easy, some insulation an air gap and more insulation, coupled with a heat shield.

    Exhausts will run cooler if it's optimized for efficiency. This means equal or nearly so pipe runs, mandrel bends, possibly taking advantage of scavenging and other "tricks" such as port matching, multiple angle valve seats, chamber and port polishing, etc. Improved exhaust flow gets out of the pipe faster, so you have less absorption. Once you've improved the efficiency, you can wrap the pipe(s) with rockwool, which is far better than 'glass. Around this a stainless screen to hold it on, then an air gap and heat shield (sheet metal), which also gets wrapped, but with a "dissimilar" material composite, such as DynaMat. I've done 12 HP air cooled engines to 400 HP liquid cooled V-8's and I can touch the exhaust 12" away from the port without getting burned.

    Air alone even if forced, isn't going to help much and will do nothing for noise. The only time air works, is when the exhaust pipe is extremely short (a few inches), no restrictions (so much for a muffler) and you have a huge volume of air, flowing over the pipe. Piston driven aircraft engines get away with this, but some have been known to spit out these little pipes, if left to idle too long on a taxiway.

    Remember it's about the two types of noise and heat, plus what the exhaust needs. Most boats have very inefficient exhausts, but it's cool enough to be acceptable in a compartment. So, clean up the exhaust paths, improving flow, then keep the heat in the pipe, as long as possible (more efficency stuff), then contain, disperse and absorb the remaining noise and heat.
     
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