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Technical Fuel line size effect on pressure?

Discussion in 'The Hokey Ass Message Board' started by c-10 simplex, Jun 14, 2019.

  1. F-ONE
    Joined: Mar 27, 2008
    Posts: 1,685

    F-ONE
    Member
    from Alabama

    Back in '66 Bobby Allison plumbed his roll cage tubing as a fuel line. The officials took note as he could run several laps without pitting.
    Back then they only weighed car before the race. Another thing he did was fill his roll cage with BBs. He had a trap door that let the bbs out. Each lap he was getting lighter and lighter. The officials took note when they noticed BBs everywhere.
     
  2. Which in a fuel system with carburetors will be the needle seat.

    Think not just radial PSI but think in bore size equations. I know pies are round but PIE R Squared area of 1/4” line times the given PSI vs area of a 1/2” line times same PSI. That’s actually the force shoving the fuel thru the needle seat.

    Or shoving air into your air tools to do some work.
     
    Last edited: Jun 19, 2019
  3. Pressure?
    Line size?
     
  4. F-ONE
    Joined: Mar 27, 2008
    Posts: 1,685

    F-ONE
    Member
    from Alabama

    I may be mixing stories. I know the BBs or lead shot trick was in the 60s probably 66 when he ran his Chevelle in Nascar. He probably got that idea from the Great Escape when the prisoners dumped tunnel dirt out of their trousers. After that Nascar started weighing cars before and after the race.

    The Tube chassis fuel line may have been in the 80s. Nascar wanted the fuel line ran inside the tube. What they did was cap the 2" or 3" tube (whatever they used) and used the actual tube chassis as the fuel line. The chassis actually became part of the fuel reserve.
    Technically it was not against the rules.
    As far as pumps or pressure I have no idea.
     
  5. ekimneirbo
    Joined: Apr 29, 2017
    Posts: 131

    ekimneirbo
    Member
    from Brooks Ky

    Yes, the needle seat will be the smallest orifice when using a carb....but you have to realize that the fuel reaching the old block mounted mechanical pumps was gravity flow, and after the pump its a pressure flow. An orifice that has pressure forcing a liquid thru it can flow as much or more than a larger orifice (the fuel line) with no pressure. The idea though is to furnish more fuel to the pump than it will ever use.
    You also must consider that many Hot Rods have multiple carbs so they have multiple orifices to satisfy....but still only one gravity fed fuel line.
    Using an electric in tank pump helps prevent vapor lock and fuel starvation problems and always insures an adequate supply of fuel. It can be adjusted to provide more pressure if necessary. So the fuel system must have more flow capacity whether pressurized or not, than the carb can use....then the needle valve becomes the limiting orifice.
    That said, there have been millions of cars produced that operated just fine with gravity fed and carbureted systems, but many were plagued with "vapor lock". Remember the old "clothes pin" trick.

    Anyone interested in air fittings, here is a neat video showing the differences.
     
    Last edited: Jun 19, 2019
  6. gimpyshotrods
    Joined: May 20, 2009
    Posts: 15,935

    gimpyshotrods
    Member

    I use Milton V fittings in my shop, and at work. The do make a noticeable improvement, even with 3/8" lines, with 1/4" NPT fittings.

    They are backwards-compatible, too.
     
    ekimneirbo likes this.

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