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Thread: AFR numbers

  1. #1

    AFR numbers

    I'm going to be doing some testing on my new setup tomorrow and was wondering what are good AFR numbers to have at different rpm. thanks for your help.

  2. #2

    Join Date
    Aug 2006
    Gonzales, La
    I've noticed that the stocker runs 12.5/1 at idle, 14.5 at intermediate speeds, and 12.5/1 again at full throttle. These are probably good safe numbers, though max power comes around 13/1.


  3. #3
    fabrication guru rapidacceleration's Avatar
    Join Date
    May 2005
    Lake Travis austin, TX
    with the......
    rr ecu
    external IC
    10lbs greenwheel
    and 42lbs injectors

    of course it hard to stare at the mirror at high speed but...........
    i see approx..
    12.0 @ idle
    12.2 @ 4000
    13.4 @ 6000
    13.2 @ 8300

  4. #4
    West Texas RXP skoepp's Avatar
    Join Date
    Oct 2007
    west texas
    Quote Originally Posted by miamirider View Post
    I'm going to be doing some testing on my new setup tomorrow and was wondering what are good AFR numbers to have at different rpm. thanks for your help.
    Good question.

    With the above 2 comments, then when do you want to change your AFR. I mean do you change it based on WOT rpms reading or at mid throtle readings.

  5. #5
    Focker Foggy's Avatar
    Join Date
    Oct 2007
    Olathe KS
    You seem a little fat (rich) in lower rpms and a little lean up top.

    Are these rpms at WOT or just at cruising -- ie: part throttle,
    because that makes a big difference in where you want to be at.

  6. #6
    Website may not be suitable for small children WOT's Avatar
    Join Date
    Mar 2007
    You want rich at full throttle only. At part throttle (no boost) there is no advantage to running rich. You are just wasting gas. At full throttle, you need to be around 12:1 or richer for sustained full throttle application. A rich mixture offers carbon dillution during the burn cycle and staves off detonation. Detonation under boost is very destructive.

    Some of you may notice that this seems kinda rich when you compare it to how you might set up a turbo car, etc. It seems you can be at 12-13:1 on the car and it is really no problem. The difference is in how long you will be at full throttle. With a 1000 hp car, you can't be at full throttle for more than say 15 seconds or you will be doing over 200 mph. On a pwc, you tend to just pin it back and stay there for a while.

    The reason for the necessity to run rich on a ski or boat is the heat load in the motor. A rich mixture staves off detonation. The more heat load in the combustion chamber, the more likely the detonation. A 10 minute wot run really gets everthing heat soaked (pistons, rods, crank, oil temp, cyclinder walls, everthing, and detonation is much more likely when everything is hot. That is the primary reason boats, skis, etc need to be rich at wot, but automobiles typically are set a bit more lean. If you were just doing 10-15 second blasts, 13.5:1 would be fine.

    Ideally, we would be setup to run 13:1 at full throttle at first stab, then the controller would add fuel in say 5 second increments settling in at 11.5:1 or so after 20-30 seconds. Since our fuel controllers don't do that, I would stay rich to stay safe.

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