manifold why are they different on boats

Discussion in 'Jet Drives' started by jarredpeter, Oct 31, 2012.

  1. jarredpeter
    Joined: Oct 2012
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: adelaide

    jarredpeter Junior Member

    my understanding of a car manifold isn't cooled down so why does a boat need water through manifold to keep cool. only asking cause i have been looking at getting a twin carb for my 186 and was wondering if a car manifold would work?

    cheers
     
  2. TeddyDiver
    Joined: Dec 2007
    Posts: 2,582
    Likes: 124, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    Car engine get's a lot air to cool the engine and thereabouts, in boat it's in a cramped poorly ventilated hole under the cabin sole..
     
  3. Petros
    Joined: Oct 2007
    Posts: 2,936
    Likes: 148, Points: 63, Legacy Rep: 1593
    Location: Arlington, WA-USA

    Petros Senior Member

    Who ever told you that is not that familiar with engines. This is not entirely true, almost every auto manifold circulates coolant through it, but not to cool it but rather to keep it warm enough to prevent icing of the throttle plate. when pressure drops across the throttle plate moist cool air can develop ice deposited. Coolant circulating around the throttle area will prevent ice from forming in the intake and around the throttle. This same is true about marine engines as well. A build up of ice will make it hard to keep running.

    It doubtful that you are cooling the intake manifold on a marine engine either, there is no reason for it to get hot. Both automobile and marine engines heat the intake manifold. Many even have electric heating elements under the carb to prevent icing up before the engine warms up.

    There is no reason the intake manifold needs to be cooled, it has cool air coming into it. Many older cars, and marine engines, even have direct contact with the exhaust manifold to keep fuel from pooling inside the intake manifold. this happens with carb engines when cold since it is running rich and carb/manifold are cold. Evaporating the liquid fuel out of the low places in the intake manifold actually can improve economy, but also reduces emissions of un burned fuel.
     
  4. DCockey
    Joined: Oct 2009
    Posts: 4,929
    Likes: 455, Points: 83, Legacy Rep: 1485
    Location: Midcoast Maine

    DCockey Senior Member

    Are you talking about intake or exhaust manifolds?
     
  5. TeddyDiver
    Joined: Dec 2007
    Posts: 2,582
    Likes: 124, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    Good point..
    Thou bcs of the reasons I said can't see much use for intake manifold with, nor exhaust manifold without circulation in a boat..
     
  6. jarredpeter
    Joined: Oct 2012
    Posts: 7
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: adelaide

    jarredpeter Junior Member

  7. Petros
    Joined: Oct 2007
    Posts: 2,936
    Likes: 148, Points: 63, Legacy Rep: 1593
    Location: Arlington, WA-USA

    Petros Senior Member

    the picture is of a combined intake and exhaust manifold. they used to do this on old automobile engines too, it is just obsolete by modern standards. Heating the intake manifold actually reduces efficiency of the engine, cold air is more dense and will make more power and better economy (efficiency). but cold air also has the icing problem in cooler climates, and now with strict auto emissions requirements, the intake air temp is very closely controlled along with mixture. Good mixture control is not possible with an intake manifold designed like the one in the link.

    On a boat there is no reason to combine the two manifolds other than to prevent carb ice. This old design is more compact and perhaps a bit lighter than conventional modern intake manifold and separate cast iron exhaust, but at the cost of a much more efficient design by modern standards.
     
  8. WestVanHan
    Joined: Aug 2009
    Posts: 1,374
    Likes: 56, Points: 0, Legacy Rep: 746
    Location: Vancouver

    WestVanHan Not a Senior Member

    Non crossflow head with siamesed ports aka reverse flow head.
     

  9. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 480, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Yes, automotive intake manifolds work just fine on a boat. Automotive exhaust manifolds also work fine, but the engine bay has to be wide open to the air, to let out the heat. Headers are the same story. If the engine bay is closed, you'll need water cooled exhaust manifolds.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.