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  1. #1
    Professional Alike Racer Clazz. Teerayoot's Avatar
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    Fuel Presure Drop at WOT ,is this situation normal ?

    I try set fuel pressure at 55psi @idle as Riva suggest on Stage III+,

    fuel pressure not same at idle ,it begin decreasing when near and WOT,
    (i will check for number tomorrow)

    1000CC duty circle not above 100%,around 80%

    MAP sensor max i can see is 218 kPa (16psi?)

    Top speed 75GPS

    so might have another question ,why such that much boost ,but so low top speed

    Thank.


  2. #2
    SHOBiz's Avatar
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    There is no way those injectors should really be at 80% dc. I would check the config file and or send it off to Pete along with a log.

  3. #3
    Professional Alike Racer Clazz. Teerayoot's Avatar
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    Quote Originally Posted by SHOBiz View Post
    There is no way those injectors should really be at 80% dc. I would check the config file and or send it off to Pete along with a log.
    I 'm Vi-PEC gang !

  4. #4
    SHOBiz's Avatar
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    Quote Originally Posted by Teerayoot View Post
    I 'm Vi-PEC gang !
    Then send it to Riva (don't remember the guys name)

  5. #5
    hitman's Avatar
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    You are probably going to have to log the voltage to your fuel pump to make sure it is correct.

  6. #6
    Professional Alike Racer Clazz. Teerayoot's Avatar
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    Quote Originally Posted by hitman View Post
    You are probably going to have to log the voltage to your fuel pump to make sure it is correct.
    I'm not sure how to log fuel pump voltage.

    Any other clue to make Fuel pressure drop while in WOT?

    I'm going to replace stock Fuel Pump with R&D High Flow,

    but has no anyone mention at all about stock fuel pump limit,
    except Fuel Regulator.

    Thank for every reply and suggestion,
    i'm try to join 80mph+ club ,but unable yet

  7. #7
    hitman's Avatar
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    Quote Originally Posted by Teerayoot View Post
    I'm not sure how to log fuel pump voltage.

    Any other clue to make Fuel pressure drop while in WOT?

    I'm going to replace stock Fuel Pump with R&D High Flow,

    but has no anyone mention at all about stock fuel pump limit,
    except Fuel Regulator.

    Thank for every reply and suggestion,
    i'm try to join 80mph+ club ,but unable yet
    Have you talked to R&D about the issue? I would do that before ordering any parts. The problem may very well NOT be the pump. It could be an issue in the wiring harness or one of a few other things.

  8. #8
    Phil.Borg's Avatar
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    Your fuel pump voltage drops as your rpm increases try setting up your fuel reg to raising rate

  9. #9
    desperado's Avatar
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    Quote Originally Posted by Teerayoot View Post
    I try set fuel pressure at 55psi @idle as Riva suggest on Stage III+,

    fuel pressure not same at idle ,it begin decreasing when near and WOT,
    (i will check for number tomorrow)

    1000CC duty circle not above 100%,around 80%

    MAP sensor max i can see is 218 kPa (16psi?)

    Top speed 75GPS

    so might have another question ,why such that much boost ,but so low top speed

    Thank.
    Yes it is normal. Why......? Because the stock fuel pump does not have the flow capacity to feed a 325hp+ engine running 1000cc injectors. Further, fittings and connectors inside the fuel tank have inside diameters less than 3/16".... not good. Typical fuel pressure drop at WOT on an E1 engine is 15%. So, if pressure is set at 55psi, it can drop very quickly in the 46-48psi range. If you substract intake boost pressure of 15psi.... then net fuel pressure at the tip of the injector is 31psi-33psi... Not good.

    Many people have a tendency to increase injector flow volume when they see high injector duty cycle in their log files. This is like putting the cart before the horse. A good fuel system starts with a good fuel pump -- one that has sufficient flow volume to hold pressure at any injector duty cycle. So, if you have installed a set of 1000cc injectors, a properly matched fuel pump should deliver and hold a steady 55spi at 4000cc flow rate per minute (1000cc X 4 injectors @ 100% duty cycle)..... anything less is a compromise and will require you "tweak" your tune file to provide for fuel system design issues.

    The bottom line is 1000cc injectors are a patch for lack of fuel pump flow volume in most cases for ski's setup for up to 16psi boost. This boost level requires no more than 750cc injectors @ 80% duty cycle when properly fed with 58psi fuel pressure and where engine speed does not exceed 8,800rpm.

  10. #10
    305coco's Avatar
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    very good explanation desperado, thanks for sharing.

    the online store here lists 2 different fuel pumps one is 255 lph high pressure fuel pump, and the other is 255 lph LOW pressure fuel pump, whats the difference??
    wich one would correct the issue teerayoot is having ?

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