Question about fuel line sizes

Discussion in 'Small Block Tech' started by 71custconv, Aug 1, 2019.

  1. 71custconv

    71custconv Active Member

    I have a 71 skylark 350 4bbl. Does anyone know off hand what the factory fuel line diameters are? I think I have a 3/8 tank to pump supply line and a 5/16 return line and a third line that is smaller that may be a vent line. The reason I am asking is that I am considering a holley spread bore (quadrajet replacement) sniper EFI. Holley recommends a 3/8 supply line and a 5/16 return line minimum. I was hoping to use the original steel fuel lines if possible. I am building this car for the wife and would like to give her the dependability of EFI.

    Thanks
    Jay
     
  2. Swagon

    Swagon Well-Known Member

    my car had 5/16th feed lines. Right now im running -8(1/2") feed and -6(3/8") return probably overkill but it definitely handle pretty much anything I throw at the car.
     
  3. alec296

    alec296 i need another buick

    3/8 is supply , I believe return is 1/4 .
     
  4. 71custconv

    71custconv Active Member

    Thanks I am hoping that with a stock 8.5-1 350 that the 3/8 will supply plenty of gas. I may have to run new a return line, or use the stock return and vent lines together for the return. I am trying to keep the EFI "hidden" as much as possible. I think the GS breather should do a good job hiding it, lol.
     
  5. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I would run a -6AN push lock hose for the return. The 3/8" stock line should give you plenty of fuel. I have a single -8AN push lock hose supplying my 470. I used the Robb Mc sender with dual -8AN lines. You might want to consider that,

    https://www.robbmcperformance.com/products/1069_gmsend.html
     
    Donuts & Peelouts likes this.
  6. 72gs4spd

    72gs4spd Well-Known Member

    A 3/8 line will be fine. The inner diameter of the line will be close to the 1/4” NPT fittings on most pumps. I almost have everything I think I need to convert to EFI myself. Going with the Holley Super Sniper, Tanks Inc tank with cut corners and their 340lph pump. Going to install 3/8” stainless lines and PTFE lined hoses. Thinking of going with Hot Rod Fuel Hoses and fittings. The hoses and time are all that’s holding me up. Current motor pretty much stock, but not the next one, so it’s a lot of overkill. Next spring should be interesting.
     
  7. vfdsrcreeby

    vfdsrcreeby New Member

    Can someone happen to tell me what the sizes are for the two hard fuel lines on the motor?? I thought I had measured these as 3/8" but cant get a 3/8" fitting into the female side,,, its too big 2nd photo. Maybe 5/16?? pulled and sold my motor so cant do it myself.

    Thanks
     
  8. sailbrd

    sailbrd Well-Known Member

    If your feed line is in perfect like new condition it should be more than enough to feed the stock 350 or most street mods for that motor. I personally hate push lok type hose. If you want to set up a fuel system to never worry about all but the hard line should be PTFE.

    Now to the return line. The return line should be at least as big as the feed line. Fuel pressure is controlled by the amount of fuel returned to the tank on return style fuel systems. I have set up two Fitech systems on supercharged BBB's running 700 hp. Mine has -10 return Bobb's has -8 return. Both feed with -8.

    With your motor you could be better off with a returnless style fuel system. Get on the Sniper of Fitech pages and see what is being done there. This would let you hide more of the FI stuff.
     
  9. Schurkey

    Schurkey Silver Level contributor

    All "rubber" hose is somewhat porous. Using an excess of rubber hose leads to fuel stench in the garage after being parked all night.

    1. Don't use more hose than absolutely needed. Use steel tube or the sort of hard-plastic tubing used by the OEMs. Double-wall seamless steel tube is less expensive, lighter, longer service life, less prone to rock damage, etc. than hose.

    2. I'm very fond of the PTFE (Teflon) liner hose such as Aeroquip 2807, or the hot-rod version of that product. Expensive, but easy to build, non-porous, doesn't react with common automotive chemicals, and good heat resistance. Some folks want a conductive-plastic liner, I've never used the conductive version.
     

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