Stage 1 fuel pump……return line….1/4 mile help

Discussion in 'Street/strip 400/430/455' started by Canadian GS 350, Aug 11, 2021.

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  1. C.Rob

    C.Rob Well-Known Member

    I would say your pretty much maxed out do to engine horsepower. My stock 70 with a little cam like yours went 96-98 mph. Felt faster and 3:42 but too end it was a pig.
     
    C.Rob, Oct 19, 2021
    #21
  2. Ken Mild

    Ken Mild King of 18 Year Resto's

    What's the exact function of the return line anyway? Why is it even necessary?
     
    Ken Mild, Oct 20, 2021
    #22
    Mark Demko likes this.
  3. Mark Demko

    Mark Demko Well-Known Member

    Keeps the fuel cooler by returning some to the tank, more so on a/c equipped cars
     
    Mark Demko, Oct 20, 2021
    #23
    Ken Mild likes this.
  4. Schurkey

    Schurkey Silver Level contributor

    It's considered a VAPOR return. The hose may be 1/4", but the outlet in the pump is restricted to perhaps .030 or .060. Point being, if the fuel boils in the suction plumbing, the pump can eject the vapor/fumes back to the tank while still supplying liquid fuel to the carb. The tiny orifice doesn't pass much liquid, but passes vapor readily.

    Vehicles with A/C tended to have more problems with vapor lock, so the engineers put a vapor return system on them by the early/mid '60s or even before.
     
    Schurkey, Oct 20, 2021
    #24
    chrisg and Ken Mild like this.
  5. Ken Mild

    Ken Mild King of 18 Year Resto's

    Okay so the goal was if it is pinched off, whatever it was allowing to drain back is left in there as extra supply in the case of starvation?
     
    Ken Mild, Oct 21, 2021
    #25
  6. LARRY70GS

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

    If you close off the return, the pump has a bit more capacity to deliver fuel. When I ran the Stage1 pump, I had a ball valve in line with the rubber line so I could open and close it.

    See post #3 on page 1 of this thread.
     
    LARRY70GS, Oct 21, 2021
    #26
  7. Mark Demko

    Mark Demko Well-Known Member

    Kinda puckers things up, like trying to fart, but yah cant
     
    Mark Demko, Oct 21, 2021
    #27
    Ken Mild likes this.
  8. Ken Mild

    Ken Mild King of 18 Year Resto's

    So did you find you were starving but when you block it off it actually helps and prevents starvation? I was able to solve that problem at WOT with secondary metering rod change. But my car is not quite as ballsy as yours. Also one time I was totally nosing over shortly after upshift into second and the whole issue was related to the fact that I had less that a quarter tank of gas. Never imagined that would be the case but I guess it was pulling pretty hard and sloshed it all away from the sump.
     
    Ken Mild, Oct 21, 2021
    #28
  9. LARRY70GS

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

    I'm talking about my original iron engine, not my current engine. I don't remember it making a noticeable difference. My engine always ran pretty cool thanks to the Griffin radiator, so vapor lock was never really a problem for me. I would shut it off, especially in the winter, when I didn't need it. It is the kind of thing that MIGHT make a difference if you were on the edge. Or, maybe not.

    If you are wondering about your fuel delivery being up to snuff, then you need to monitor fuel pressure. Either fit your car with a permanent gauge, or rig up a temporary one so you can see where the pressure goes under high demand.

    For a temporary check, you might tee into the fuel line using components like this,

    https://www.jegs.com/i/JEGS/555/15270/10002/-1

    https://www.jegs.com/i/JEGS/555/41010/10002/-1

    https://www.jegs.com/i/JEGS/555/41057/10002/-1

    Tape the gauge to the windshield and go for a drive.
     
    Last edited: Oct 21, 2021
    LARRY70GS, Oct 21, 2021
    #29
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  10. Ken Mild

    Ken Mild King of 18 Year Resto's

    What is an appropriate fuel pressure reading at idle and at WOT? I'm sure it ranges....but for a mechanical Stage 1 fuel pump on a 430 HP car....?
     
    Ken Mild, Oct 21, 2021
    #30
  11. LARRY70GS

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

    6-7 psi at idle. Should not go below 4 psi at WOT I'd think.
     
    LARRY70GS, Oct 21, 2021
    #31
  12. Ken Mild

    Ken Mild King of 18 Year Resto's

    Funny I wouldn't think the pressure would go down at WOT but I guess that's why I am not an engineer. :D I would think it would be like oil pressure, going up with RPMs.
     
    Ken Mild, Oct 21, 2021
    #32
  13. LARRY70GS

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

    First, the engine is consuming fuel at a maximum rate, and the pump needs to keep the float bowl(s) full. Look at the flow in gallons per hour between the Stage1 pump and the Robb Mc 550 Pump,

    FuelPumpFlow.JPG

    Look at the flow between 0 pressure, and flow at 4.5 psi. At 0 pressure, pump flow goes up with RPM. When it has to maintain pressure though, flow starts to go down at higher RPM. As the car accelerates harder, the fuel pump has to suck and push fuel against the generated g forces. That's not even mentioning an engine that flows more air and needs more fuel than the pump can provide. The Stage1 pump is good to about 450 HP I believe.

    Look at TA Performance's recommendations,

    FuelPumpRequirements.jpg
     
    LARRY70GS, Oct 21, 2021
    #33
    Ken Mild likes this.
  14. 87GN_70GS

    87GN_70GS Well-Known Member

    For the Stage 1 pump, 40 gph at 6k rpm and under load (4.5 psi) it will support 40 x 6 lb/gal ÷ 0.5 lb/hp-hr or 480 hp
     
    87GN_70GS, Oct 22, 2021
    #34
  15. 87GN_70GS

    87GN_70GS Well-Known Member

    My Robbmc pump is about 8.5 psi at idle and drops to about 6 psi at WOT, supply enough fuel for 590 hp.
     
    87GN_70GS, Oct 22, 2021
    #35
  16. Canadian GS 350

    Canadian GS 350 Well-Known Member

    It was easy to do Larry’s shut valve mod in the return line. I will not know if it will make any difference at all until I’m back at the track in the spring. I suspect this low compression small valve small cam stock exhaust manifolds 455 is just maxed out at 95 mph end of the quarter mile. Trap speed is an indication of hp……all in all, 13.94 quarter mile time is not bad for what it is. I have new drag radials - 275/50/15 on 8 inch rims with 5.5 BS (which fit great). I was running a tired set of bias ply ss streets. These should hook better than the tired bias ply I had.
     
    Canadian GS 350, Oct 22, 2021
    #36
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