Marine (ized) engine horsepower loss over time

Discussion in 'Gas Engines' started by Red Tide, Oct 19, 2009.

  1. Red Tide
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    Red Tide Junior Member

    OK, time for my overly broad question of the day today:

    I'm wondering how many horsepower is a normal gas sterndrive engine expected to lose as the hourmeter ticks by...

    Let's say a carb engine sportboat used 100 hours a year on weekends. The owners are a typical family who have the boat serviced once or twice a year by a marina mechanic.

    If the engine starts life at 300 hp when brand new, what would you expect this average mercruiser or volvo gas "car" engine to have for horsepower after 5 years and 500 hours of running in typical recreational use?
     
  2. FAST FRED
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    FAST FRED Senior Member

    "If the engine starts life at 300 hp when brand new, what would you expect this average mercruiser or volvo gas "car" engine to have for horsepower after 5 years and 500 hours of running in typical recreational use?"


    YES , the reason is the car engine RATED at 300 hp will last an hour or two at that rating , BUT operated normally at 150hp (15gph) or at times 200hp (20gph) the service life will be almost 2,000 hours if maintained and not abused.
    The bit of full throttle dragging a cruiser up on the plane is no problem (10-15 seconds) IF the engine is at operating temp.

    Will there be some power loss from leaky valves , ignition not spot on , or crud in the fuel , OF COURSE , but with the % throttle used at std cruise , a tiny bit more wont be noticed.

    FF
     
  3. BHOFM
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    BHOFM Senior Member

    A new engine will improve for the first 1/3 of its life, then hold for 1/3 then
    start a slow decline over the last 1/3.

    Two stroke engines improve for about 1/2 of their life, decline quickly.

    This is for engines that operate in normal conditions with proper care.

    The air filter is the key to engine life.
     
  4. CDK
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    CDK retired engineer

    Look at GM's industrial engine site to see how the particular engine is rated. It will be much lower than 300 hp of course because the industry is not interested in fiction but in facts. At the given rating the engine has a substantial service life and even at the end, when the oil consumption tells the owner it is time for something new, the power output hasn't changed noticeably.

    The Mercruiser rating is something totally different.
    It means "we want you to believe that this engine could deliver 300 hp, but it doesn't, it just sounds good and you probably wouldn't have bought it if we told you the truth".
    500 Hours and 5 years later, nothing has changed.
     
  5. Red Tide
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    Red Tide Junior Member

    As opposed to a flame arrestor alone?
     
  6. Red Tide
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    Red Tide Junior Member

    Glad to hear the longevity of "car" engines professionally adapted for marine use is a lot better than I had feared. Looking at the GM website, they rate their OEM vortec marine at 292 hp
    http://www.gm.com/experience/technology/gmpowertrain/engines/specialized/marine/2010_5700_Marine.pdf
    while the block for industrial use on different fuel is rated at 216 hp
    http://www.gm.com/experience/techno...ecialized/industrial/2010_5700_Industrial.pdf
    which I suppose is continuous, but the different fuel confuses me when making a comparison...
     
  7. TollyWally
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    TollyWally Senior Member

    "we want you to believe that this engine could deliver 300 hp, but it doesn't, it just sounds good and you probably wouldn't have bought it if we told you the truth".

    LOL, that's a fact. I have a gas motor rated at 330 hp. The real motorhead guys at a dragboat site I sometimes frequent have told me it might top out at 280 on a real good day. With the carb adjusted the way it is now I am topping out at 220 or so.
     
  8. apex1

    apex1 Guest

    There is no air filter on a marine engine! Just the flame arrestor.
     
  9. broke_not
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    broke_not Junior Member

    Industrial engines are always rated lower, but it isn't necessarily because there's anything "fictional" about the non-industrial engine ratings. The big difference in the hp numbers is there because the industrial version typically has its hp "rating" taken at around 4000 rpm. That doesn't mean it isn't capable of producing more hp, it simply means that the equipment it's marketed towards, (genset/pump/whatever), requires a power spec at a given rpm that will give a reasonable service life.

    It would be silly to rate non-industrial engines the same way. If a car or light truck engine is designed and built to be able to produce, say 275 peak hp at say, 5000 rpm.....what would be the point of "rating" it at 4000 rpm? Alternatively, what would be the point of listing a peak hp rating achieved at 5000 rpm for an industrial engine that would never see 5000 rpm?

    A peak hp rating doesn't mean it's fictional.



    ;-)
     
  10. Frosty

    Frosty Previous Member

    Max Hp is different from the Marine rated because the marine rated is constant.

    Constant output is the Hp that it is designed to give for hours -days on end.

    Something a marine engine is often required to do, rather than a minute at a time whist changing gears in a truck.


    Marine Engines don't have filters?? Do you mean need or have?
     
  11. Red Tide
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    Red Tide Junior Member

    The question of air filters is one I have not considered -- now that you mention it I think I've seen what looks like air filters on larger gas EFI engines. On my gas carb engines I've only ever had the metal screen flame arrestors. What would get sucked through those screens to damage the engine? My bilge usually contains a little water, a tiny bit of grease, and maybe a tiny tiny amount of sand/debris carried by shoes or from the cockpit when working on the engines, but I don't think that would be sucked up. Maybe around the beach around sanddunes there would be hard particles in the air? I'm curious what the air filters do on a boat if people are using them...

    --A swarm of tiny gnats?
     
  12. CDK
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    CDK retired engineer

    This discussion has come up several times already.
    What Mercruiser sells as a marine engine is an old-fashioned GM block painted black. The materials used and the half a century old design make it unsuitable for the advertised output power if longevity is required.
    The engines did well in passenger cars when fuel efficiency was no consideration. Speed limits and the ever present automatic gearbox kept these engines from reaching more than 3000 rpm except for a few seconds. As industrial engines they still do very well because the low rpm seriously reduces the power output so a long service life is obtained.

    The concept "marine engine" is too wide. A real marine engine is of course a diesel with 2 stage cooling, designed for or adapted to a long life propelling a boat. Such a performance cannot be expected from the gasoline engines this thread is about.
    In a recreational GRP boat they are reasonably reliable because a year generally means one holiday plus a few weekends and the owner, once he is familiar with the fuel bills, pulls back the throttle to 3500 rpm or less. Again the actual power output is at or below the industrial rating.

    A different situation develops when these engines are used for the propulsion of heavier vehicles like cabin cruisers that stay in the water most of the year. The weight/power ratio and marine growth forces these engines to do hard labour and premature engine failure is at the horizon.
     
  13. broke_not
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    broke_not Junior Member

    All well and good, but that still doesn't mean that there's anything "fictional" about the advertised power output.....which is what you said a few posts up.

    There it is right there. "We want you to believe this engine could deliver 300 hp, but it doesn't...."

    Sorry, but it does.

    You can post up a couple of long, meandering paragraphs in response if you like, but unless you edit what you've already posted....it's going to come off as back-pedaling.

    I'm just sayin'....

    ;-)
     
  14. CDK
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    CDK retired engineer

    You must be a Brunswick shareholder. Sorry I offended you.
     

  15. broke_not
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    broke_not Junior Member

    Not offended, nor am I a Brunswick shareholder. (Although I do find the "Brunswick shareholder" comment a little offensive. Does someone not sharing your opinions automatically mean they have some monetary motivation?) You made a couple of statements that were delivered in a pretty matter-of-fact manner. But they were just opinions.....and that's all.

    Remember this thread?

    http://www.boatdesign.net/forums/gas-engines/carb-fuel-injection-conversion-22495.html

    You did the same thing there. You started out with a matter-of-fact statement about fuel pump motors being brushless, but again....it was opinion more than fact. And rather than 'fessing up about the comment being more opinion than fact when some evidence to the contrary was presented, well....read the thread.

    I'm just sayin'....

    Long story short, if an engine manufacturer gives one engine a peak hp rating, and then gives the industrial version of the engine a hp rating at a lower rpm around where its intended use will be.....there's nothing fictional about either rating.

    ;-)
     
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