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Thread: How lean can you go?

  1. #1
    Potential Tuner
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    May 2013
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    How lean can you go?

    Hello. I am curious as to how lean of an afr can be safely run without damaging your engine.
    If I understand correctly, GM's own lean cruise can command 17:1 and leaner without adverse results on modern cars. I am specifically thinking of the 2004 Pontiac GTO, but I have seen evidence of some modern japanese cars running an afr of 20:1 and leaner without a problem. Obviously leaner mixtures can result in hotspots in the cylinder and lead to detonation and higher exhaust gas temperatures that I have heard can damage catalytic converters. However, what is the afr limit, or is it more of an exhaust gas temperature limit?
    Are there any other features/changes/tables that GM and other manufacturers change to allow such lean mixtures?

    Any input is appreciated.

    Sincerely,


    -Meesha

  2. #2
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    bump.

  3. #3
    Advanced Tuner Dr. Nopps's Avatar
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    "Any input is appreciated." Running a leaner mixture in the manner in which you are suggesting may result in higher concentrations of Oxides of Nitrogen in your vehicle's emissions. However, as you have seen other countries feel it's a worthy trade-off if you are consuming that much less initial pollution causing fossil fuel. If you change your COT table, only lean out the cruising portion - you wouldn't want to hold back fuel in your power range.