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Technical Fuel line

Discussion in 'The Hokey Ass Message Board' started by Blue One, Mar 14, 2018.

  1. Blue One
    Joined: Feb 6, 2010
    Posts: 8,452

    Blue One
    ALLIANCE MEMBER
    from Alberta

    Just wondering about fuel line size for my RPU
    Tim McMaster built
    309 warmed up Y block with 3 new Stromberg 97s.
    The Stromberg’s take 1/4” fuel line and I’m going to run a mechanical fuel pump with a fuel pressure regulator.

    My concern is the size of the fuel line I’ll run from the tank to the fuel pump.

    If the line from the fuel pump to the fuel block and then to the carbs is 1/4”, is there any advantage to running 5/16” fuel line from the tank to the fuel pump?

    Or, would the entire system run in 1/4” make more sense and supply enough fuel?
    We’re not talking high pressure or flow etc.
     
  2. LM14
    Joined: Dec 18, 2009
    Posts: 1,046

    LM14
    Member
    from Iowa

    I always run a size larger before the pump, always done it that way. My current car is getting 3/8" from tank to pump (my pump has 3/8" NPT fittings) and 5/16 from pump to carb (my carb has 5/16" inlet). 1/4" should work OK for a small displacement engine, that's what most had from the factory. I'm just more comfortable with the next bigger line in front of the pump.
    SPark
     
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  3. brigrat
    Joined: Nov 9, 2007
    Posts: 4,285

    brigrat
    Member
    from Wa.St.

    Bigger is better also for keeping the larger volume of gas cooler.........................................
     
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  4. tb33anda3rd
    Joined: Oct 8, 2010
    Posts: 13,198

    tb33anda3rd
    ALLIANCE MEMBER
    1. Connecticut HAMB'ers

    i have always wondered about that. if the line is big it would move through the line slower, sitting in one place longer. smaller it would move quicker and be replenished with cooler fuel from the tank. not arguing, i just always had that thought in the back of my mind. of course, a return line makes that mute.
     
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  5. Let's do this in an "if then" style question and answer

    If 1 carb requires 1/4 fuel line ,,,
    Then how big of a fuel line does 3 carbs require?

    If the Area of .25 line is .049
    Then .049 x3 = the requirements of the main line feeding 3 branches.

    .049x3 = .147
    3/8 line area is .111
    1/2" line area is .196


    You can look up some fluid flow charts too.

    3/8 would "probably" be enough
    1/2" if you plan on max effort WOT driving
     
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  6. squirrel
    Joined: Sep 23, 2004
    Posts: 39,455

    squirrel
    ALLIANCE MEMBER

    I think you might want to consider that the ID of 1/4" fuel line is pretty small.

    I'd run 5/16" in this application. If it were a bigger engine with a decent size carb on it, then 3/8" might be called for, but most car makers got away with using 5/16" line on almost all small block engines for years.
     
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  7. Gotgas
    Joined: Jul 22, 2004
    Posts: 6,485

    Gotgas
    Member
    from DFW USA

    I'd suggest 5/16 from tank to pump, and 5/16 again from the pump to the fuel distribution block. Then 1/4 to each carb.

    If you think you (or the next guy) might want 400ish hp, now would be a good chance to run 3/8 from the tank.
     
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  8. carbking
    Joined: Dec 20, 2008
    Posts: 2,189

    carbking
    Member

    Regardless of the number of carburetors, the engine is going to use a certain amount of fuel.

    Pontiac found 3/8 inch line was sufficient to fuel a 455 H.O. for all street use.

    And as posted by others, many small blocks came with 5/16 inch.

    If you use 3/8 inch, would highly suggest the use of the return line, as the larger line will cause the fuel to run slower and absorb more engine heat. The return line will help cool the fuel.

    Jon.
     
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  9. porknbeaner
    Joined: Sep 12, 2003
    Posts: 40,135

    porknbeaner
    Member

    3/8 line is what you want for a streeter. Your pump doesn't have to work as hard and the bigger line acts like a reservoir. You will always have fuel on tap.

    Here's is a little story. My old racin buddy started out with a big block dart that he street raced and sometimes grudge night at the local track. He was starving on the big end and what we did was up size the fuel line to 1/2 from 5/16 from the tank. No special pump, not trick anything just a bigger line and it solved his problem.
     
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  10. Blue One
    Joined: Feb 6, 2010
    Posts: 8,452

    Blue One
    ALLIANCE MEMBER
    from Alberta

    So far I think I like this suggestion the best for my application using the 5/16" from the tank.
     
    Last edited: Mar 14, 2018
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  11. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 3,618

    Bandit Billy
    ALLIANCE MEMBER

    3/8th to and from the regulator, 3/8's to the filter, 3/8ths to the carb distribution block. Then I knock it down to the individual carbs. Everything SS other than the final Russell braided nylon line from firewall to fuel block on blower. Probably overkill but that never stopped me.
     
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  12. Stick with the bigger line,I assume you will be running a fuel pressure regulator and that will control the amount of gas getting to the carburetors. HRP
     
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  13. rusty rocket
    Joined: Oct 30, 2011
    Posts: 2,759

    rusty rocket
    Member

    3/8ths on my sbc powered 32 sedan. Also ran a return line if i ever changed to fuel injection. DSC02788.JPG
     
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  14. Blues4U
    Joined: Oct 1, 2015
    Posts: 2,457

    Blues4U
    Member
    from So Cal

    Larger size on the supply side to the pump is standard practice for pumps of all types. I'd go with 3/8" from tank to pump, 5/16" from pump to regulator/filter/fuel log, from there you could leave it at 5/16", or step it down to 1/4". Smaller diameter line is easier to bend if you're going to get fancy with it.
     
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  15. Beanscoot
    Joined: May 14, 2008
    Posts: 449

    Beanscoot
    Member

    I've had no problems using the stock 5/16" line to feed my 351W.
     
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  16. nobux
    Joined: Oct 19, 2002
    Posts: 617

    nobux
    Member

    Go 3/8". No one ever said "I wish my fuel line was smaller."
     
  17. ROADSTER1927
    Joined: Feb 14, 2009
    Posts: 2,311

    ROADSTER1927
    Member

    On the mid 60's chevys the 348 and small blocks got 5/16" line and tank unit. The 409 got 3/8 ".:)
     
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  18. Sure A 5/16 line will feed a fuel block with 3 outlets at 1/4" sure it will, but not well.

    Look at the ID of the fittings being used because you'll get no more fuel that can pass thru that fitting- that will be the flow limiting orifice in the line. Don't matter if you have 4" line feeding that fittings ID
     
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  19. Dave 39
    Joined: Jul 24, 2006
    Posts: 53

    Dave 39
    Member

     
  20. Dave 39
    Joined: Jul 24, 2006
    Posts: 53

    Dave 39
    Member

    The word that you want here at the end of your sentence is ''moot''. A very useful word. Dave
     
  21. Only as good as your smallest fitting before the pump.......ah someone beat met to it. I would run 5/16" IF your smallest fitting ID is the same.
     
  22. Beanscoot
    Joined: May 14, 2008
    Posts: 449

    Beanscoot
    Member

    Speaking of fittings, it's worth comparing different ones from your big ol' box of fittings because some will have larger drilled holes than others, even if they are nominally the same fitting.

    You can drill the holes larger in some cases, but you have to use judgment in how far to go without getting the walls too thin.
     
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  23. Blue One
    Joined: Feb 6, 2010
    Posts: 8,452

    Blue One
    ALLIANCE MEMBER
    from Alberta

    All good info guys keep it going. After consultation with a rodding buddy today I’m leaning towards 3/8 from the tank to the pump and then 5/16 to the regulator and the log, then from the log it will be 1/4 to each carb.

    All ni cop lines.
     
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  24. Beanscoot
    Joined: May 14, 2008
    Posts: 449

    Beanscoot
    Member

    Man, I wish my fuel line was smaller.
     

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