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  1. #1

    Understanding fuel duty.

    If fuel duty is at 100% and you cannot hit the target AFR (still too lean), will increasing the fuel pressure help?

    I realise that blanket raising the fuel pressure will screw with all the other AFR's, but I can take fuel out at those places.

    So assuming raising pressure would work, when should you increase injector size and back the pressure off again?

    Running stock #48's at 59psi (cause I can hit 58 on the dial!!)

    What is considered good practice for injector duty %?

    Finally, which injectors would help me with my mod level and not screw up my idle?

    Trying to learn, not just get a part number.
    Last edited by tornado34; 07-11-2014 at 01:57 PM.


  2. #2
    Quote Originally Posted by tornado34 View Post
    If fuel duty is at 100% and you cannot hit the target AFR (still too lean), will increasing the fuel pressure help?

    I realise that blanket raising the fuel pressure will screw with all the other AFR's, but I can take fuel out at those places.

    So assuming raising pressure would work, when should you increase injector size and back the pressure off again?

    Running stock #48's at 59psi (cause I can hit 58 on the dial!!)

    What is considered good practice for injector duty %?

    Finally, which injectors would help me with my mod level and not screw up my idle?

    Trying to learn, not just get a part number.
    Generally, you get concerned whenever the DC exceeds 85% I always replace the injectors and restart tuning whenever the DC exceeds 90%

    Idle quality is is not a problem on the VT11 injectors. I run them on a stock motor. My idle fuel pressure is 60 PSI. At WOT, it drops to about 58 PSI.

  3. #3
    JT jpt7779's Avatar
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    I am using ID 1000cc injectors and on WOT 8800-8900 rpm runs my injector duty cycle is usually around 70-71%. FPR set static at 58 psi.

    http://www.4-tecperformance.com/inde...oducts_id=1929

  4. #4
    dpracing's Avatar
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    VT11's here. No drivability concerns to report.

  5. #5
    Boost addict hotbird's Avatar
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    80% DC at 20 psi and 8900rpm here.
    Stock pump, riva rrfpr, set to static pressure. Turbo.

    IMO if your at 100% DC at 58-59 psi you need to upgrade the injectors and or check fuel pressure at wide open throttle.

    Running 90% or above can be dangerous when the weather cools back down.
    Last edited by hotbird; 07-11-2014 at 09:30 PM.

  6. #6
    Keep in mind that you need to have the base tune in your ECU set up for the opening time of the injectors. Each brand has somewhat different caricaturists. There are settings in the ECU that need to be set.

    Note that a 1000cc in brand Y can require very different settings for a 1000cc in brand Y. The spray pattern can also be very different.

    Andy

  7. #7
    Sanfish's Avatar
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    Quote Originally Posted by whittlebeast View Post
    Idle quality is is not a problem on the VT11 injectors. I run them on a stock motor.
    Idle 1700? Was there a noticeable increase in fuel consumption?

  8. #8
    Bob 1tommygunner1927's Avatar
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    What fuel pump is in use? There was great debate on different pumps and the use of a relay.

  9. #9
    boost junkie skidoochris's Avatar
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    why would bigger injectors raise fuel consumption
    you need to have the correct tune for every injector
    the bigger injectors are needed if your injectors are in the 90s% duty cycle
    injectors run there can misfire or lock up
    also idle will not change if you have the correct tune
    v-tech has tunes for their 1100 injectors (probably actually only 950cc)
    you should never change injectors with out changing the tune in the ecu

  10. #10
    Quote Originally Posted by Sanfish View Post
    Quote Originally Posted by whittlebeast View Post
    Idle quality is is not a problem on the VT11 injectors. I run them on a stock motor.
    Idle 1700? Was there a noticeable increase in fuel consumption?
    Yes, the idle is a rock solid 1700 on both the Motec or the Vtech. Fuel economy is for more based on how much you are hammering on the throttle than the AFR. I personally did not buy a $15000 ski and hang several thousand dollars of electronics on it to save fuel. I did it for rock solid and instantainious throttle respanse, no matter where the motor was in the power band when I nail it.

    I came from a 35 year road racing background when I purchased the RXPX.

    Andy

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