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Thread: What afr for best cruise/idle gas mileage (closed loop)

  1. #1
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    What afr for best cruise/idle gas mileage (closed loop)

    So the stock ecu while in closed loop will adjust to try and maintain 14.7 afr. Since I have dual wbs on the car I was thinking about using them to simulate nbs and fake the ecu into thinking it's adjusting for 14.7 when it's really something leaner. If you are wondering, I have innovate wbs that allow you change the scale of the analog output.

    Does anyone have any experience on what afr will actually net better gas mileage?

    I've seen a chart on Jeff's site which shows a little over 16 nets better gas mileage but at the expense of higher nitrogen oxides. Looking up catalytic converts it seems that 14.7 is where it's efficiency is best so I assume that is why 14.7 is used. I uhm, don't run a cat (shhh)... So I'm not sure what's worse, producing more nitrogen oxides or more hydrocarbons...That is a different discussion of course

    What are the consequences? Yes I know I could probably just lose weight and gain more but if I attempt this and reduce weight on top then it's even more. I'm also wondering if this would allow running colder plugs without them fowling out as easy when cruise/granny driving.

    What are any other side effects? I assume overheating might be an issue?


  2. #2
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    go as lean as you can without making it hesitate. when cruising you're not burning that much gas, so exh. temps and cylinder pressures should be fine.
    Maddog Performance Engineering

  3. #3
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    yeah the only thing you may fight with having the stock ecu trim the fuel is going up hills it is still going to be lean and may try to knock.

    If you unplug the narrowbands and use a tuning tool with wideband tracking you can avoid this by tuning based on MAP.

    Parting 6 speed
    Pampena 3.5 Stroker, GTX 2867 Gen IIs, AEM Series2, oohnoo SMIC, DN Hardpipes, FIC 1650s, Walbro 525, aermotive fpr, Dejon intake pipes, Tial Q, Koyo Rad, Samco Hoses, Stoptech 332mm fronts, HKS GT4 Coilovers, Spec 4+ LW, JDM 6 Speed, Billet shift forks, Pampena brace


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