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FMU vs AFPR

Posted by 95'RS-T, May 28, 2009

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  1. 95'RS-T

    95'RS-T Proven Member

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    Joined Mar 10, 2009
    Germansville, Pennsylvania
    ok found a good price on a 255lph hp pump from extreme psi all i need now is the 12:1 fmu I was wondering what the difference is between the Fmu and AFPR but at the same time i believe I'm answering my own question by saying the AFPR is constant pressure even at idle, thus creating too much fuel correct? I know the fmu uses vac/boost so it then raises and lowers the pressure when off and on the throttle right?
     

    378  0

    1995 Mitsubishi Eclipse GST
    · 2G DSM
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  2. LD25Delta9

    LD25Delta9 Proven Member

    606
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    Joined Feb 12, 2008
    Ft. Wayne, Indiana
    You are correct. Unless you have a way to tune some injectors, the FMU is the way to go. I would reccomend a Walbro 255HP instead of the 255LPH if you plan on going crazy with boost. They have minor differences, but the HP has a higher pressure threshold.
     

    714  0

    1997 Eagle Talon N/T
    manual · 2G DSM
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  3. Locke

    Locke N/T DSM Wiseman

    2,683
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    Joined Jan 1, 2005
    Houston, Texas
    An AFPR is an adjustable 1:1 FPR. The 1:1 is only to keep an adequate pressure differential between the fuel and atmosphere in the intake, so the injector will spray will spray with an acceptable pattern.

    A FMU allots full flow under boost, which is why it must supplement a real FPR, but with a high gain ratio such as 12:1 or 10:1. In this case, the added fuel pressure is used to increase flow through the injector in a proportion to boost in an effort to adequately fuel the motor.

    A SFMU is a FMU who's static fuel pressure is adjustable, along with interchangeable springs and disks to alter the gain and rate of gain.
     

    808  0

    1999 Mitsubishi Eclipse N/T
    manual · 2G DSM
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  4. LD25Delta9

    LD25Delta9 Proven Member

    606
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    Ft. Wayne, Indiana
    I wish there was a smiley for getting a bitchslap....cause I'd post one on myself for that!
     

    714  0

    1997 Eagle Talon N/T
    manual · 2G DSM
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  5. 95'RS-T

    95'RS-T Proven Member

    438
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    Joined Mar 10, 2009
    Germansville, Pennsylvania
    ok i got the FMU AFPR situation ;) i was just wondering if i could use a AFPR instead of a FMU but i think i'll just stay with the 12:1 FMU and 255HP pump
     

    378  0

    1995 Mitsubishi Eclipse GST
    · 2G DSM
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  6. Locke

    Locke N/T DSM Wiseman

    2,683
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    Joined Jan 1, 2005
    Houston, Texas
    Use an AFPR when an ECU will be controlling fuel in boost, such as with MegaSquirt.
     

    808  0

    1999 Mitsubishi Eclipse N/T
    manual · 2G DSM
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  7. rstare

    rstare Proven Member

    777
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    Joined Jun 9, 2008
    Winthrop Harbor, Illinois
    If your planning on using a 12:1 fmu at all, with the basic "Star" setup and 8psi, you need a Walbro 255lph hp pump.
    You can do the calculations :)
    [​IMG]

    Edit: Be aware that the chart is in GPH, not LPH.
     

    852  0

    1997 Mitsubishi Eclipse N/T
    manual · 2G DSM
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  8. david-b

    david-b Proven Member

    367
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    Joined Aug 15, 2005
    Chicago, Illinois
    Going a little off topic but still close... what about a SFMU with MS instead of a AFPR? With a 1:1 disc?
     
  9. Locke

    Locke N/T DSM Wiseman

    2,683
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    Joined Jan 1, 2005
    Houston, Texas
    A 1:1 SFMU would function like an AFPR.
     

    808  0

    1999 Mitsubishi Eclipse N/T
    manual · 2G DSM
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  10. david-b

    david-b Proven Member

    367
    2
    Joined Aug 15, 2005
    Chicago, Illinois
    Excellent. That's what I wanted to hear.
     

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