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Boost reference Fuel Pressure Regulator or not?

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    Boost reference Fuel Pressure Regulator or not?

    So, I'm using an Aeromotive 13132 fuel pressure regulator in my turbo stroker build here. It has a boost/vacuum reference port which is connected to my intake manifold.



    We set the fuel pressure for 45 psi with the car off and MAP reading 100 KPa. I noticed that at idle, with MAP down to 40 KPa, fuel pressure gets pulled down to 35 PSI. This makes sense.

    However, Megasquirt VE tables already have fuel adjustments for RPM and MAP. Do I even need to have the FPR boost/vacuum referenced? Seems like it will interfere with the MS.

    ??
    "And then we broke the car. Again." Mark Donohue, "The Unfair Advantage"

    Das Beast build thread

    #2
    And of course, one Google search after posting this I found the answer here.

    "If you want the injectors to be linear in their fuel delivery then yes you should vacuum reference the FPR. When there is vacuum in the intake this makes the pressure across the injector greater as the engine vacuum is literally sucking on it. So you need the FPR to reduce rail pressure with increasing vacuum. This means the effective injector fuel pressure stays the same under all operating conditions."
    "And then we broke the car. Again." Mark Donohue, "The Unfair Advantage"

    Das Beast build thread

    Comment


      #3
      Injectors work in differential fuel rail pressure. Fuel pressure should be a constant 43.5 psi (3bar) above intake manifold pressure. Too little differential pressure and the injectors won't spray properly; moreover, they'll spray less fuel. Too much and they'll never open, but the advantage of having more pressure is more fuel—assuming you can compensate for the longer injector dead time and lower fuel pump flow.

      Most small pressure changes can be compensated by the VE table (usually measured in fuel load %, not 'pure kpa' values)—large changes in pressure become harder to compensate for, especially if fuel pressure is unpredictable. Small changes can be tuned out or handled with closed loop fuel control. If you have static fuel pressure you will effectively lose some tuning resolution.

      In the simplest terms, leave it the way it is and tune ignoring fuel pressure unless you can't get enough fuel at the top end and high load areas.


      Edit: smh I guess I should refresh before crafting a response. Glad you found your answer!
      '84 318i M10B18 | 93whp/90ftlbs | 147- Safari Beige | MS2E w/ LC, 2-Step

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        #4
        This is the same reason RRFPRs are a stupid idea. Tie it to the manifold, you want a 1:1 injector response to make tuning possible.
        Build thread

        Bimmerlabs

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          #5
          Nando WTF? 33,461 posts? :devil:
          "And then we broke the car. Again." Mark Donohue, "The Unfair Advantage"

          Das Beast build thread

          Comment


            #6
            Yeah, that's like 16 years of posting. not even counting e30sport.net which was before this :p
            Build thread

            Bimmerlabs

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