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Supercharged Nytro AFR differences with hood off

Discussion in '4 Stroke Turbos/Supercharger' started by Krummy, Dec 31, 2017.


  1. Krummy

    Krummy Extreme

    Messages:
    53
    Country:
    USA
    Snowmobile:
    2009 FX Nytro
    I went up for the first time this year thinking I had cured my fuel issues from last year with a new inline pump and FPR. After taking it out at 8.5 psi, I am still seeing 12.7-13 AFR at WOT. I then went to adjust my blow off valve and kept the hood off during testing. I took it out and started getting cruise AFR in the 9's which had never happened before. I then took it out for a blast with the same boost and saw AFR's in the 11.5-11.8 range WOT. I then put my hood back on and my WOT AFR's went right back to the upper 12's to 13. I am at a loss as to why the AFR's would be drastically lower with the hood off rather than with the hood on. Does anyone have any thoughts on this? Ultimately I am thinking I will need to upgrade to PCV-PTI with 430cc injectors but I am still confused why it ran so well with the hood off and why the numbers were so different.
     
  2.  
  3. YukonMP

    YukonMP VIP Member VIP Member

    Messages:
    377
    Location:
    Yukon Territory
    Country:
    Canada
    Snowmobile:
    2011 Yanaha Bravo LT
    2014 Yamaha MultiPurpose
    Maybe the intake air flow is smoother with the hood on, turbulent and therefore less efficient with it off. Be warned this is a complete guess by a total novice.

    No charge.
     
  4. Krummy

    Krummy Extreme

    Messages:
    53
    Country:
    USA
    Snowmobile:
    2009 FX Nytro
    Haha, yeah it just doesnt make any sense to me. It is a supercharger with a cold air intake over the clutch gaurd. I am wondering if one of my boost reference lines for the fpr, gems, or koso gauge is getting kinked by the hood and if that would change these numbers
     
  5. peppahillcustom

    peppahillcustom Extreme

    Messages:
    57
    Location:
    mass
    Do you have a fuel pressure gauge inline after the pump? Your fuel pump can change pressure flow slightly from the heat under the hood, on my setup I see a 2 to 3 lb difference from when I start it cold to running at idle warmed up. The pump can heat soak. I always set my fuel pressure on a warm motor
     
  6. yamadoo

    yamadoo Yamadoo is a snowmobile ' aholic'. Lifetime VIP Member VIP Member

    Messages:
    2,999
    Location:
    SE MN work North shore Superior play
    Country:
    USA
    Snowmobile:
    15 Viper STX DX red/white
    13 Apex XTX 45 anniversary RED/WHITE/BLACK
    10 Vector LTX Blue
    10 vector GT- White 10,000miles for sale
    11 Venture Gt
    I’m with Yukonmp in both theory and expertise, I suspect with hood off there is a significant difference in air flow direction and pressure
    Again no charge for this opinion based on old physics and pulmonary (lung) air flow training. LOL
     

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