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Thread: Propane...Good or Bad

  1. #1
    Join Date
    Mar 2009
    Location
    Las Vegas
    Posts
    208

    Default Propane...Good or Bad

    I've been told that running straight propane gives better milage, is this true and what needs to be done to the motor to make it work on propane? Can you keep the motor to work on gas once you switch it to propane? Anyone who's done this before, please chip in your $.02 on the Pros/Cons.
    '71 Basterd Scout 2
    with a 258 from a '73 CJ5
    Intake manifold with NHRA markings....go figure

    "Its (scout) four-wheel-drive capabilities are equal to anything this side of full tracks"

    David H. Petraeus for President 2012

  2. #2
    Join Date
    Feb 2009
    Location
    Aiken, SC
    Posts
    2,423

    Default

    The engine runs cleaner on propane. You do not get better mileage, but sometimes propane is cheaper. I think you get about 15% less per gallon, but if you save 20% per gallon, that's still a savings.
    The total advance must be limited, I think to about 22 degrees.
    There are kits for this so you can switch back and forth if you want. They run about 400-800 bucks.
    The SV engines used to have propane intake manifold gaskets. These were only different in that they did not allow the flow of exhaust through the warm up passage. If the gaskets are no longer available, you'll just want to remove the flapper.
    The biggest drawback is fuel storage. That tank has to go somewhere. Not so bad on a pickup truck, you can use a 75 gallon tank in the bed, but in a scout, a pair of 15 gallon bottles takes up some serious room.
    Allan E.
    Curmudgeon Extraordinaire
    Charter Member, Old Hippie IH Club
    Old fashioned binder freak

  3. #3
    Join Date
    Oct 2009
    Posts
    6

    Default

    on a avarge about 1/3 gallons more of prop, then gas.

  4. #4
    Join Date
    Oct 2009
    Posts
    29

    Default

    My brother is trying this on a 345. He has the kit but is on hold in the process for a few reasons.
    First he is looking for a specific intake manifold. I can't remember which one. I think he called it a flare bore.
    When I got my 392 rebuilt they asked me what kind of rings I wanted. They gave me 3 different kinds. Cast iron, moly, and LP/natural gas. Which brought the question; Do you have to have LP/natural gas rings? I thought LP/natural gas rings were cast iron.
    Then there is the legal issue. A company will sell the kit but advertise them as not street legal. I guess it depends on the state and the kind of bottle you have? I am fuzzy on the legal stuff.
    I am also told that if you want similar fuel economy to gas and the engine to run really good, the compression needs to be around 9.5.
    The engine will run cleaner, cooler, last longer, and produce similar power and slightly less fuel economy. From what I am told (I have not tried LP).
    Just my spare change.

  5. #5

    Default

    you can get alot of info from gotpropane. com

  6. #6

    Default

    on propane you wont stall out when going up steep grades like you will with a carb

  7. #7
    Join Date
    Mar 2009
    Location
    Las Vegas
    Posts
    208

    Default

    Ok then, it looks like I might put propane on my next engine build.
    But can you run propane, then switch over to gas without changing your carb/manifold out?
    '71 Basterd Scout 2
    with a 258 from a '73 CJ5
    Intake manifold with NHRA markings....go figure

    "Its (scout) four-wheel-drive capabilities are equal to anything this side of full tracks"

    David H. Petraeus for President 2012

  8. #8
    Join Date
    Oct 2009
    Posts
    16

    Default

    ive seen kits in the past that let you run propane or gas by just flipping a switch...A propane unit simply bolted on the air filter lid (a flat looking unit) in which would dispense the propane into the carb when you hit the steep terrain. And supposed to run with a stock motor with no need of these specail rings, think it was called "affordable propane" or something like that.

  9. #9
    Join Date
    Oct 2009
    Posts
    5

    Default Running on Fumes

    My 78 Terra ran on propane for the first 20 years until I bought it. It's 304
    V8, 4WD, auto and air. Mine had the switch for gas or propane under the dash. I got around 8 mpg with propane vs 12 to 14 if tuned right with gas. I removed the whole assemble and retuned for gas.
    Propane had a lot less HP too. And I was never to comfortable about the big bomb riding right behind me in the bed.

  10. #10
    Join Date
    Oct 2009
    Posts
    16

    Default

    Quote Originally Posted by Rons78Terra View Post
    My 78 Terra ran on propane for the first 20 years until I bought it. It's 304
    V8, 4WD, auto and air. Mine had the switch for gas or propane under the dash. I got around 8 mpg with propane vs 12 to 14 if tuned right with gas. I removed the whole assemble and retuned for gas.
    Propane had a lot less HP too. And I was never to comfortable about the big bomb riding right behind me in the bed.
    id like to take that stuff off your hands if you still have it??

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