Upgrading to 3/8 fuel line

Discussion in 'Fuel and Air Systems' started by wafastr, Jun 24, 2018.

  1. wafastr

    wafastr Active Member

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    Doing a restomod on a 70 dart, s6 to 360. Considering a 3/8 fuel line with no vapor return line. Also wondering if the stock tank, with its factory 4 hose vapor vent system, would work okay with an unvented factory style painted gas cap. I think it should be okay. Any advice out there?
     
  2. 67Dart273

    67Dart273 Well-Known Member

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    The 4 tank vents that year were designed to go up to the vapor separator tank in the trunk. If you eliminate that, and just hook one or more to a vent of some sort, you may create a "puke" or "siphon" situation. If I were in your shoes I would put a vent line branched into the filler tube like the non CA 70 and the 69/ earlier cars. This was simple and works well.

    What is not clear in this diagram is that the vent tube bends up and goes clear up to the top of the quarter panel, then down along the filler tube, through the gasket, and open ends just inside the rear frame rail

    2cmugso.jpg
     
  3. Murray

    Murray FABO Gold Member FABO Gold Member

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    3/8" is only for race cars. You're wasting your time on the street. Removing all the vapor vent system and installing a vented cap should work as far as I know.
     
  4. Biff

    Biff Well-Known Member

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    500 hp +. 3/8 fuel line
     
  5. Murray

    Murray FABO Gold Member FABO Gold Member

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    I apologize- yes on 3/8" line.
     
  6. Biff

    Biff Well-Known Member

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    All good bud ... we’re all friends here!
     
  7. 67Dart273

    67Dart273 Well-Known Member

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    I would not run a vented cap. Construct a proper vent system, not that hard. And then you don't have to worry about gas puking down the side of the fender
     
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    • wafastr

      wafastr Active Member

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      I will stay with the 5/16" fuel line. A Hemi or dual quad big block may need a 3/8" line but probably not a 360. Would the existing vapor vent system work well enough to allow fuel to flow to the fuel pump and adjust for expansion in the fuel tank if I just cover the end of the vapor line (that originally went to the s6 breather cap) with screen to allow air movement in that line? Thanks for your replies.
       
    • 67Dart273

      67Dart273 Well-Known Member

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      You could. Leave the line HIGH to prevent siphon. Another thing you could do is tee it into the breather to the filter bonnet. Will help keep fumes at bay
       
    • yellow rose

      yellow rose Doctor of Thinkology.

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      If I was going to all the trouble to make new fuel lines I wouldn't bother with 3/8 line. I go right to 1/2 and be done. A bigger fuel line won't hurt you. Ever. Especially if you are using a mechanical pump.
       
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      • 67Dart273

        67Dart273 Well-Known Member

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        Unless he's building a 600+hp monster, that is overkill. The size alone is enough to discourage me, 1/2 is much more difficult to work with, and I used to fiddle with HVAC service, back in the day. I still have my 3/8, 1/2, and 5/8 benders, and may have a 3/4 somewhere
         
      • yellow rose

        yellow rose Doctor of Thinkology.

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        If you use aluminum tubing it bends real easy. Steel tubing...not so much.
         
      • dusted

        dusted FABO Gold Member FABO Gold Member

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        If the lines need replacing (kinked, rusted thru, bent ) then upgrade to 3/8. If they are fine then stick with 5/16 and use the money saved somewhere else in the build. Just my opinion.
         
      • 73hcode

        73hcode Well-Known Member

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        I have a question it might be stupid but when you go to a 3/8” line what mechanical fuel pump do you use.
         
      • dusted

        dusted FABO Gold Member FABO Gold Member

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        Good point, I’m running an electric pump so I have 3/8 fittings. Most cars ive seen with the 3/8 line have 5/16 to the carb
        Some of the mechanical hp pumps come 3/8 and others have removable fittings, in which case you would size the fittings accordingly.
         
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