Questions about Robb MC 550 Fuel Pump

Discussion in 'The Mixing shop.' started by Cutlass, Dec 29, 2020.

  1. Cutlass

    Cutlass Platinum Level Contributor

    as always interested in your real life experience:
    1. what size for the low pressure fuel line (tank to pump) do you guys have installed to provide for a 500HP motor?
    2. any disadvantages in not running a vapor return line?
    THX, Ralf
     
  2. LARRY70GS

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

    According to the instructions, for engines over 450 HP, you should use 1/2" (-8AN) from tank to pump. If you do not use the vapor return feature the pump will make 1 psi more pressure, about 8 psi. With it installed, it will make about 7 psi.

    https://www.robbmcperformance.com/products/buick550.html

    My CV products pump makes 8-9 psi and I have occasionally seen 10 psi. My Q-jet and AED carburetors don't seem to mind one bit.
     
  3. 71stagegs

    71stagegs bpg member #1417

    I run one works great 1/2 pick up 1/2 line to pump with return 7lbs
     
  4. 87GN_70GS

    87GN_70GS Well-Known Member

    Mine makes about 9 psi at idle, Qjet was fine with it. Drops to about 6 psi under WOT feeding 586 hp. Video:


     
  5. Cutlass

    Cutlass Platinum Level Contributor

    Thanks guys!
    @ Larry: Jim mentioned the CV pump, but I am a little shy due to the price tag.
    W/ or w/o vapor return line
    W/ or w/o vapor return line and what size pick up line?

    I am in need of a little education here:
    In what mode of operation is the thirst of the motor the highest? At high engine rpm, close to peak HP, or thru out the whole rpm range, at WOT?
     
  6. Briz

    Briz Founders Club Member

    Have the RobbMc 550 on the Riv's 430. With the 3/8 line it would starve for fuel around 4500 RPM. Pulled and modified the sender to 1/2" Ran 1/2" hard line all the way to the front of the car and reused the stock 3/8 as return. Have not had an issue again.
     
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  7. 71stagegs

    71stagegs bpg member #1417

    Ralf i run stock return line its always at 7 lbs and over at idle. I had a stage 1 pump with stock line half way thru 2nd it nosed over changed to RobbMc pump 1/2" sender 1/2" line to the pump It pulls hard now
     
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  8. LARRY70GS

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

    At WOT, at highest engine load, at highest RPM, in other words, at the top end of the track on a 1/4 mile pass.
     
  9. 87GN_70GS

    87GN_70GS Well-Known Member

    Vapor return line is capped off. Pick up line is 1/2".

    Pump flow falls off as rpms climb, but fuel demand increases
    Screenshot_20201230-144713_Chrome.jpg
     
  10. Brett Slater

    Brett Slater Super Moderator Staff Member

    Dumb question: when you say you ran 1/2 inch line, did you replace the entire factory fuel line from the tank to the fuel pump?
     
  11. Cutlass

    Cutlass Platinum Level Contributor

    Thats what I am going to do.
    To me it does not make sense to have a 1/2" pickup and to still restrict the flow/volume by keeping the stock 3/8" fuel line.
    At a given pressure in a line, there is more volume/time flow, the bigger the diameter is.
    And given the length from tank to pump, the low pressure line is quite a restrictor in the system.
     
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  12. LARRY70GS

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

    I used push lok hose from tank to pump. Aeroquip FC598 hose with AN fittings.
     
  13. Briz

    Briz Founders Club Member

    I did just that. If ya look close you can see the copper line run from a filter in front of the R R wheel well all the way up to behind the RF wheel. The rubber 1/2 line goes into a factory hole in the frame, up through a clip in the spring pocket, through the cross member out another hole and into the pump. So it is true 1/2" all the way from the bottom of the tank. Could not find a sock for the pick up so its made longer towards the back and put a metal filter in line


    96519333_10221045304095999_7954615564922519552_o.jpg
     
  14. 436'd Skylark

    436'd Skylark Sweet Fancy Moses!!!!!

    It's easy enough to leave the factory lines in place and run a new line. I ran a braided 1/2" line for the feed and repurposed the factory 3/8" line as my return line. The original return line is still in place unused. I added the robb mc 1/2" sender while I was there..
     
  15. DasRottweiler

    DasRottweiler -BuickAddict-

    I may be replacing my 3/8 factory feed line, so I was looking for options. My return is 6an, running Holley Blue Pump on rear frame rail. RobbMC sending unit, 8an stainless to 3/8 hardline .
    I used Aeroquip push-lock for my transmission lines that I ran through the frame and had intended to use it for fuel feed line. Then I came across this,
    https://ls1tech.com/forums/fueling-...socketless-hose-fc598-anyone-else-issues.html
    I may just go with stainless 6an. I don't feel as though my 450-500hp requires 8an...Jim
     
  16. Cutlass

    Cutlass Platinum Level Contributor

    Joe, that is exactly what I will do. What level of pain was it to route the braided line? Did you route it close along the stock lines? I already have purchased Dash 10 PTFE steelbraided line, as this is close to 1/2" inner diameter. Outer diameter is 0.64" and I hope it will feed thru the openings of the frame.
     
  17. 87GN_70GS

    87GN_70GS Well-Known Member

    I called inline tube and ordered a 1/2" hard line
     
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  18. LARRY70GS

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

    I ran my -8AN push lok through the frame. It really wasn't bad. I have a word document on running the line, that I got from Jim Weise that I can't post here, but I can e mail it.
     
  19. Brett Slater

    Brett Slater Super Moderator Staff Member

    What was the turn around and how was the fit?
     
  20. Brett Slater

    Brett Slater Super Moderator Staff Member

    1/2 inch sender being the sock less unit for the tank?
     

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