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Thread: AFR Question

  1. #1
    MPower's Avatar
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    AFR Question

    Just wondering if anybody has any idea what the AFR is for a 255 motor running a 4" intake and no flame arrestor in the intake mani.


  2. #2
    West Texas RXP skoepp's Avatar
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    Here was one of my test on T-X back last Fall.



    70 air, 77 water, 29.8 pressure, 59 dew, 2,200 ft = 3,800 ft RAD

    T-X
    added 84 ring and saw exact same speeds, no change, 10.0 psi boost at 8,060 with flashes of 8,080 rpm.
    So was better RAD and going from 85 to 84 same rpm with same speed.
    72.5 to 73.5 mph. I did notice that the prop almost wants to come on hooked with this ring, not sure tho, as i tried to repeat and it hooked good. It felt faster top end but GPS says no.

    my mods for any that want to know when looking at AFR:
    4 inch front air without filter, no filter in manifold, relocated X ic, j pipe with gibson. stock ecu and X sc.

    AFR readings ( 2 different recordings)
    warmed up ski good, then 1st recordings:
    idle - 12.9-13.1
    2,500 rpm - 12.1
    3,000 rpm - 11.9
    3,500 rpm - 12.0
    4,000 rpm - 12.5
    4,500 rpm - 12.8
    5,000 rpm - 13.2
    5,500 rpm - 12.9
    6,000 rpm - 13.1
    6,500 rpm - 12.5
    7,000 rpm - 12.4
    7,500 rpm - 12.1
    8,000 rpm - 11.7
    8,060 rpm - 11.5

    After that recording i made some speed runs for a good while and noticed that it was starting to lean out more with some high 13,s to even low 14,s when cruising say 60 mph.
    So i let the ski cool down a bit ( 5 minutes) and did another recording.

    idle - 13.3
    2,500 rpm - ?
    3,000 rpm - 12.5
    3,500 rpm - 12.7
    4,000 rpm - 13.1
    4,500 rpm - 13.6
    5,000 rpm - 14.1
    5,500 rpm - 13.8
    6,000 rpm - 13.8
    6,500 rpm - 13.1
    7,000 rpm - 13.1
    7,500 rpm - 12.9
    8,000 rpm - 12.6
    8,060 rpm - 12.4

    I am pretty sure that the sensor was not messing up as after riding it still was calibrated correct.

  3. #3
    Site Admin Green Hulk's Avatar
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    It's perfectly normal for the afr ratio's to be in the 13's at cruising speed.
    The engine is not under load and this makes for better cruise speed fuel economy and lower emissions.

  4. #4
    MPower's Avatar
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    Awesome info as usual Steven

    So it appears those numbers look pretty good, right?

  5. #5
    West Texas RXP skoepp's Avatar
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    I was pleased with them, so never checked them again. Would have be good to recheck this winter but I am not running a j pipe anymore and dont have bung in exhuast manifold.
    THat test was last fall in 70 degrees so I would guess would be bit richer in heat of summer.

    Thats One reason i havnt added more boost or rpm, or atleast thats my excuse for right now until i get bung in mani..

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