Fuel line size...

Discussion in 'Street/strip 400/430/455' started by WQ59B, May 14, 2018.

  1. HotRodRivi

    HotRodRivi Tomahawks sighted overseas

    So todays so called AN fittings, the only thing in comon with the old original is the 37 deg taper of the flare.?
     
  2. Schurkey

    Schurkey Silver Level contributor

    "Military/Aerospace/Aviation Grade" and "Industrial Grade" use the same 37 degree taper, the same thread sizes*, and the same--or similar--internal passage sizes.

    They're downward-compatible, you can use the expensive stuff to substitute for the less-expensive line, but you'd have (legal) problems if you tried to use the less-expensive stuff on aircraft. You could even screw an Aerospace fitting onto an Industrial hose end--or the other way around.




    *Some (not all) thread sizes are ALSO shared with 45 degree flare fittings, such that Aeroquip made or still makes hose ends with a sealing radius instead of a sealing flare, so the same hose end could be used on 37 degree flares OR 45 degree flares.
     
    dan gaither likes this.
  3. WQ59B

    WQ59B Well-Known Member

    Here's my deal- factory 20-gal tank & original sender. No room to put a larger line thru the orig sender, as the tank hole is only 1 5/8-in in dia.

    So I made up this contraption; have to cut a hole in the tank top then seal this aluminum plate down- only way I can tighten the fuel fitting nut that will be inside the tank. No way to get a wrench inside when the fitting nut is 1 1/8-in. I think it'll work well. On the underside is a huge washer that I drilled & tapped, then split into 2 halves so I can feed them thru the sender hole individually. It will sit immediately 'southeast' of the sender hole, in the flat there.

    3rd pic compares the stock 1/4-in pick-up line and the -10 AN 1/2-in fitting.
    DSC05261.JPG DSC05263.JPG DSC05264.JPG
     
    Last edited: Jul 21, 2018
    patwhac likes this.
  4. WQ59B

    WQ59B Well-Known Member

    Cut the tank hole, drilled, made a rubber gasket, all fits well. Going to slip the half-round steel pieces inside the tank; the screws will point up & they are threaded into the half rounds- to brace the tank area there and make it easier to get the hardware on.
    DSC05292.JPG DSC05293.JPG
     
    patwhac likes this.
  5. HotRodRivi

    HotRodRivi Tomahawks sighted overseas

    That looks good! You will be able to hear it piss into your tank, even better!
     
  6. WQ59B

    WQ59B Well-Known Member

    That brings me right around to the final tank/fuel question- the fuel return (the black & blue fitting above is the supply).

    Read a couple topics here on return lines, would like a final answer as I want to permanently install the tank. I vacuumed out the inside from the metal shavings, but thinking if I install a bung for a return line, going to have to do that/rinse it again.

    455 Stg 2 SE, Holley 4150 carb, (will be) RobbMC 550HP pump. Running -10 AN / 1/2-in ID braided line from the tank to the pump, going to use an inline filter before the pump.
    RobbMC pump has 1/2-in NPT port for a return line. Should I use that port & run another -10AN (or -8 AN) line back to the tank? I'm one of those people who'd rather do it right the first time & not have to revisit the installation to correct a problem in the future.

    And no; I'd prefer not to hear the return dribble- was hoping to get a line down to the bottom of the tank. Can I simply drill a hole in the top of the tank, install a fuel-resistant grommet and push a steel line thru it into the tank?
     
  7. Schurkey

    Schurkey Silver Level contributor

    The vapor return was commonly 1/4". Fuel supply was 5/16" or, on some vehicles, 3/8". That is probably 5/16".

    Not unless you connect a drop from that fitting to the bottom of the tank, preferably with a strainer to filter out large particles.

    -10 is nominally 5/8", not 1/2". Actual inside diameter would be less.
    -10 is wild overkill for fuel supply at ~600 hp. Some guys like wild overkill. I think it's wasted money. Consider the actual inside diameter (flow area) of the hose or tubing. Now think about the flow area of two needle-and-seat assemblies.

    Use the minimum amount of hose possible. Preferably PTFE-liner hose, not rubber. Rubber is porous, you'll smell gasoline as if there were a leak when the car parks in the garage. Most of your plumbing should be metal tubing (NOT copper) or hard plastic like the OEMs are now using.

    I'm not familiar with that pump. Does it have a built-in regulator? "Vapor returns" can be quite small--as said, typically 1/4". The aftermarket return-style regulators will require return plumbing that can match the supply side for capacity, as nearly all the fuel pumped will be returned to the tank at idle or coast.

    Very bad idea from both a tank-pressure and safety perspective.
     
    Last edited: Sep 4, 2018
  8. WQ59B

    WQ59B Well-Known Member

    See attached pic. My original sender is out of a '59- ID is 1/4-in.

    See attached pics. -10 AN fitting ID is .494, or 1/2-in. All conversion factors and internet charts aside - anyone is welcome to measure a known AN-size fitting themselves; the tape doesn't lie.

    It probably is- motor isn't even begun to be built yet- who knows exactly where it will end up at. If it's regulated and doesn't blow the needle off the seat, I'm not sure what the harm is. I read one account here where a guy said his fuel system plumbing came in at around $1K. As is I'm at $320, and the fuel pump is $200.

    Many here were against hard line- I have a 1/2-in ID PTFE-lined braided hose. It will be 1 piece from the gas tank to the fuel filter (up by the engine compartment). There is no repro (bigger) fuel line avail, and a number of people didn't like AL for a fuel line. I can bend & flare just fine... if a consensus rises to use AL line for supply, I'll use the braided as a return.

    Site doesn't specify if internally regulated. Claims output is 7 PSI +/-1 thru the full RPM range. Site chart claims circa 85 GPH @ 6000 RPM whereas a Stock Stage 1 pump is 40 PSI. Pump has a 1/8-in NPT return port.

    Not sure how it would be an issue from a pressure standpoint- tank is vented to atmosphere via a hose. And a -say- brazed bung wouldn't create less of a pressure change vs. a grommet- I just haven't heard testimony RE if a grommet is feasible or not.

    DSC05294.JPG DSC05295.JPG DSC05296.JPG
     
    Last edited: Sep 4, 2018
  9. Schurkey

    Schurkey Silver Level contributor

    Yes, but tubing is measured by OD not ID. Hose is more-or-less the equivalent of tubing, the flow area is similar if not identical.

    So -8 hose is nominally 1/2", and 1/2" nominal is plenty huge enough. But it's your money.

    Yes, I'd be happier with double-wall seamless steel tubing, but I don't know where to get it in sizes larger than 3/8.

    1/8 NPT doesn't sound large enough for a proper return system. Vapor return, maybe. As I said, I'm not familiar with that pump. I suspect there will be instructions included with the pump paperwork.

    If venting isn't a concern, collision/rollover fuel leakage is.
     
  10. 1969RIVI

    1969RIVI Well-Known Member

    Here's my .02 cents as I just had to run a return line to my tank and spent alot of time on here asking questions and on the net researching. I drilled a hole I the top of the tank and used fuel safe washers etc. Like you are to pinch it to the tank. I then ran a short 12" piece of rubber fuel line to my new aluminum hard line. The AL return line runs the length of the car beside the supply line up to the passenger front fender well. From there I have 2 braided lines both under 36' going to and from the pressure regulator. My fuel filter is before the reg. and the pressure gauge is after the reg before the carb. ALL my lines are 3/8" both supply and return. I can't even hear the fuel "pissing" into the tank and I was advised not to put a drop tube into the tank from the return fitting because it would cause another condition cavitation/airation of the fuel and pump if I can recall what my mechanic said??? Someone can correct me if I'm wrong or close to right!! Anyways hope this helps, Cheers!!
     
  11. jr_

    jr_ Well-Known Member

    Did you use robmc fuel pump as well? If so, any fitment issues with the factory line and robmc pump?
     

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