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Thread: Fuel Economy - 2-Stroke Carburated Vs New Technology

  1. #1

    Default Fuel Economy - 2-Stroke Carburated Vs New Technology

    Greetings, what with the price of fuel going ballistic, Iím thinking about re-powering but having trouble with the numbers.

    I have a 30' aluminum ocean boat that weighs about 8,000 - 8,500 lbs fully loaded with fuel, water, gear, food, kids, and dogs - my biggest fuel saving initiative is to pack up the troops and head out for at least 3 days or more if I can swing the time off work, so we head out fairly loaded. The boat has a '91 300 hp Evinrude looper. I'm getting around 1.2 - 1.4 statute miles per gallon at optimum cruise.

    I've looked over the various test reports for both 2-stroke and 4-stroke outboards and am trying to get a feel for what improvement in fuel economy I'd get by re-powering. Of course, all of the test reports are on much smaller boats with hardly any load so the numbers look great. The E-Tec folks will firmly stand by a 20% increase in economy.

    I'd like to hear real-world data on folks that have re-powered from old 2-stroke technology to either new 2-stroke technology or 4-stroke with a same horse power conversion. What increase in mileage did you realize?

    I keep coming to the same conclusion - I can buy a hell of a lot of fuel for $20k and keep running the looper until it dies. The pay off period just in fuel savings (at $5/gal) assuming a 30% increase is about 10 years, assuming that I maintain the same range that I do now...and realistically, with better economy I'd likely end up burning up the same mount of fuel in a weekend that I do now as I'd probably go further out - the SO pointed this out the other day and basically called BS on my re-powering argument.

    Thoughts and data are appreciated.

  2. #2
    Member sayak's Avatar
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    Default No data, just thoughts

    I'd say you figured things out pretty well, except for two caveats: price of injector oil rolled in, and ongoing legality of 2-stroke machines in the age of enviro guru Gore.

  3. #3

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    I have a Searunner 210 Soft-Top. I recently switched from a 150hp 2-stroke carbed Yamaha Vmax Pro to a 140hp 4-stroke Suzuki. I am not through the break in period yet and I am still playing with props but so far this how it compares.

    new outboard
    26mph = 6.5 mpg
    33mph = 5.5 mpg

    old our board
    33mph = 3 mpg

    Not to mention I am not dumping Synthetic Oil into the motor at $29.00 a gallon. I do miss the big blue cloud and the BRAAAAAPPPPP of the engine. Now it just sits back there and hums.

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    The 2-stroke E-Tec are cleaner than 4-Stroke so there is no such thing as "legality".

    If you keep to roughly 70% throttle, the E-Tecs sip the fuel. Run it up to WOT then it is the standard 10% HP fuel burn. A buddy of mine has a 90 horse E-Tec and that is how it works out, just like the info sheets on the Evinrude website.
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    I read every thing I could lay my hands on concerning fuel economy and outboards before I purchased my Optimax 200.

    In every test I read in Power Boats, The Etec's and the Opti's gave better numbers than the 4 strokes. At cruising speeds the Opti's beat the Etec's while the Etecs were quieter. The Etec's had the better numbers while at trolling speeds. One of the guys in our moose hunting party sold his Honda 200 to replace it with an Optimax after seeing the difference in acceration and hole shot and better fuel numbers last year

    Yes, syn DFI oil is expensive. But at the same time the DFI's 2 strokes do not require oil and filter changes, valve adjustments, timing belt replacements, etc.

    You pay your money and you make your choices. But unless you are going to run a motor a couple of hundred hours a year I doubt it ever makes sense to replace it to save fuel. Just run till it breaks then replace it.
    Tennessee

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    Member Akgramps's Avatar
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    Sure the new two strokes do run very clean, clean enuf to qualify for a low emision rating....But where do you suppose that oil goes that you burn through the oil injection system?

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    Moderator Paul H's Avatar
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    Unless you are running a charter, you won't burn enough fuel to pay for the repower. It's the catch 22 of older less efficient motors. You hate paying for all the fuel you're burning, but it'll still less $ to operate than upgrading to a modern power plant.

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    Quote Originally Posted by Akgramps View Post
    Sure the new two strokes do run very clean, clean enuf to qualify for a low emision rating....But where do you suppose that oil goes that you burn through the oil injection system?
    It goes out the exhaust, same as it does a 4 stroke.
    What's the difference as long as the emmission levels are as low or lower than a 4 stroke?
    Tennessee

  9. #9

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    Quote Originally Posted by MischiefManaged View Post


    I keep coming to the same conclusion - I can buy a hell of a lot of fuel for $20k and keep running the looper until it dies. The pay off period just in fuel savings (at $5/gal) assuming a 30% increase is about 10 years
    Every time I think about repowering I come face to face with your conclusion. Don't forget that $20,000 can be earning income.

    • an initial investement of $20000
    • at 5% annual interest,
    • compounded 12 times per year,
    • after 10 year(s)32,940.19

  10. #10

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    Quote Originally Posted by Snowwolfe View Post
    It goes out the exhaust, same as it does a 4 stroke.
    What's the difference as long as the emmission levels are as low or lower than a 4 stroke?
    Please explain this one to us.

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    There aren't any catalytic converters or other emissions controls on 4s o/b's, so they dump a small amount of unburned hc's out the exhaust. The direct inject two strokes also dump some hc's out the exhaust, some from oil injection, some from incomplete combustion. The overall emissions from the 4s's and direct inject 2s's is in the same range.

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    Quote Originally Posted by polywave View Post
    Please explain this one to us.
    Whats to explain? As far as I know all outboards send there exhaust gases into the water.
    It doesnt matter if the motor is a 2 stroke, DFI 2 stroke, or 4 stroke.
    There are some 4 strokes that have higher emmission levels than DFI 2 strokes.
    Tennessee

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    Perhaps some understanding of 2 strokes is needed, as part of the combustion process a 2 stroke burns oil and sends it out the tailpipe, so to speak. that is why it is neccescary to continually add oil to the oil injection resevoir.
    A 4 stroke retains its lubricating oil in the crankcase (unless its worn out) and when it is changed the waste oil is disposed of properly, not out the exhaust. Now we can all agree the new 2 strokes are efficent and clean and maybe it doesnt matter, but the burnt oil is indeed going in the water, thats lakes, rivers and oceans.! unless you run your boat in your bath tub........

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    Not arguing that the small amount of oil that is injected ends up going out the exhaust. The point is, the 4s's are not free from hydrocarbons in the exhaust, its not crankcase oil, but unburned gasoline.

    The measured emissions from the new 2 strokes and the 4 strokes is equivalent. I suppose a direct injected 4 stroke would be even cleaner, but there aren't any of those on the market.

    You can argue the point as much as you want, but what's measured coming out of the exhaust is what matters.

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    Paul stated it very well.
    Doesnt matter if the exhaust contains unburned oil or unburned hydrocarbons. The only thing that matters is what the total levels are exiting from the exhaust.

    Kind of like arguing which is heavier, a pound of lead or a pound of feathers.
    Tennessee

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    Geez...Paul as you mentioned all the modern outboards, 4 or 2 stroke have a 3 star carb rating for emision output, so yes hydrocarbons, samo-samo. Heck, Johnson still makes a carburated 9.9 hp that meets the 3 star carb rating, that makes me wonder?
    My only point on 2 strokes was, and I believe a lot of folks may not give it any thought, is the oil goes somewhere. If the oil injection system is working right a 2 stroke (modern injected type) is burning about 100/1, if you are into the throttle alot that ratio goes down (50/1 ?) So for every 50-100 gallons of fuel burned a gallon of oil is going into the enviorment? Am I a green nut guy? no, just a regular nut who thinks about these things way to much.
    I know my 4 stroke doesnt use a gallon of oil in that amount of time, if It did I would be rebuilding or replacing.

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    Just because a 2 stroke might use a gallon of oil for every 100 gallons of gas being burned does not mean all the oil is going into the water. Vast majority is being used in the combustion process.
    The DFI 2 strokes have been certified to run clean enough on the Kenai and they are also permitted in waters where "regular" 2 strokes are banned. The DFI's do not simply pump the oil they use into the water thru the exhaust.
    Tennessee

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    Default Concur

    Didja know that oil can catch fire - YES, REALLY. The 2 stroke oil becomes part of the combustion process along with the gasoline -

    A hydrocarbon is a hydrocarbon is a hydrocarbon. It becomes a different chemical makeup after extreme heat is applied. It is not still 2 stroke oil being pushed out the 1000+ degree exhaust valves any more after compression takes place.

    The oil gets burned too.

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    So no sheen on the water like the old strokers?.......
    Well, all beee darned...

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    Quote Originally Posted by Akgramps View Post
    Geez...Paul as you mentioned all the modern outboards, 4 or 2 stroke have a 3 star carb rating for emision output, so yes hydrocarbons, samo-samo. Heck, Johnson still makes a carburated 9.9 hp that meets the 3 star carb rating, that makes me wonder?
    My only point on 2 strokes was, and I believe a lot of folks may not give it any thought, is the oil goes somewhere. If the oil injection system is working right a 2 stroke (modern injected type) is burning about 100/1, if you are into the throttle alot that ratio goes down (50/1 ?) So for every 50-100 gallons of fuel burned a gallon of oil is going into the enviorment? Am I a green nut guy? no, just a regular nut who thinks about these things way to much.
    I know my 4 stroke doesnt use a gallon of oil in that amount of time, if It did I would be rebuilding or replacing.
    Gramps,

    "Oil" is made of long-chained hydrocarbons: carbon atoms linked to hydrogen atoms and other carbon atoms. That's all they are. If the oil is burned, the result is the production of CO2 and H2O. Just because you pour the oil into the reservoir does not mean it is the equivalent of just pouring it out into the water. You need to do some background research into the E-Tec engines. They do indeed burn the oil/gas mix very efficiently.
    Great spirits have always found violent opposition from mediocre minds. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence. Albert Einstein

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