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Thread: Question concerning Target AFR & E10 Stoich.

  1. #1

    Default Question concerning Target AFR & E10 Stoich.

    Hi. I ran a search, but found no answer. For example, if a person were shooting for 13.0 WOT AFR with pure gasoline at 14.7 stoichiometric, would I command a Target AFR of 12.5 WOT AFR and scale the entire Target AFR table accordingly to compensate for the stoichiometric difference when using E10 fuel?
    Last edited by Dohctor; 11-17-2020 at 02:40 PM.

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    Yes. Although I find that E10 tends to run well with pure gasoline Target AFR values. Andrew

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    When you select the Fuel Type in the Engine Parameters, doesn’t that tell the ECU what number to display as stoichiometric? If you select the Gasoline scale, won’t stoichiometric be displayed as 14.7 no matter which fuel you're using?

    Even though E10 has a different stoichiometric from gasoline, the wideband O2 sensor has no idea what fuel is being burned. It measures in stoich percentage and then is converted to the selected fuel to be displayed as AFR. So whichever fuel is selected, you have to use that fuel’s numbers for tuning (in this case, use the gasoline AFRs despite using E10 or any other mixture). When the wideband measures stoich 1.0, it then multiplies by 14.7 for the gasoline scale and displays 14.7 AFR. If the mixture burned is 15% rich, the wideband measures 0.85 stoich, multiplies by 14.7 gasoline scale and displays 12.5 AFR.

    Bottom line, tune to the AFR number for the wideband scale selected, not necessarily the fuel in the tank.
    Last edited by fj1289; 11-18-2020 at 01:53 PM.

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    Thanks for the replies. This is similar to what has come up in research. Bottom line is, there's some compensation going on in the wideband O2 and some must take place in your calculations. I get that you should rely on the wideband O2/datalog data, but you still have to compensate in the Target AFR and VE% Table to get the desired wideband O2 reading with E10, when compared to pure Gasoline. So it boils down to the same methodology.
    Last edited by Dohctor; 11-18-2020 at 03:25 PM.

  5. #5


    Yep, in the end you simply give the engine what it wants. My example is using the gasoline scale to tune an air-cooled motorcycle on ethanol based race fuel. Although stoichiometric is about 9.8 AFR, since I’m using the gasoline scale, stoichiometric will show 14.7 AFR. I think of it as translating Spanish to English.

    It prefers to be a bit richer than 12.5 AFR at WOT, and richer still on the nitrous. I don’t have to remember the stoichiometric of the fuel I’m using, just have to be aware of the yard stick I’m using to take measurements with. My engine likes to run 15% or more to the rich side at WOT, so I’m aiming for 12.5 or even 11.8 AFR on the gasoline scale - even richer on nitrous (spraying for 20+ seconds over a mile).

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    This is all correct. I wish Holley would have a Lambda option, which would eliminate all of this confusion.

    When selecting the different fuels, does is make the Fuel Flow and subsequently the VE numbers accurate? Andrew

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    I'm very surprised by some of the local hot rodders and even professional dyno tuners in my area. I was explaining that a misfire will be detected on WBO2 sensor as lean. They kept looking for truck to go rich on the dyno AFR and it wouldn't do it. Turned out their probe fell out of the turndown and on we went. I tried explaining to more than one person the fact that if I pull a plug wire and run my Sniper powered engine you'll see lean condition same thing happens at 2-Step limiter and I'd also assume high speed limiter. Spark is killed to maintain RPM, which leaves fuel and air in pipe, which shows dead lean. WBO2 sensors don't measure how much fuel is in the stream, all they measure is air. Just surprised guys who have been in the business successfully for a long time, so clueless to a basics of internal combustion engine. Be careful out there and always do your research.

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    Lambda would be such a nice feature.

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    Lambda is nice, but after learning AFR and how to set targets and understanding how WBO2 sensor works, I just think adding a Lambda table would add a whole other table of confusion for people to get lost in. The way it is now, we have VE% Table very simple and Target AFR also very simple. The modifiers can get complicated, but if you read and do research it really isn't that more difficult than setting clock on a VCR or turing the GPS on a GoPro.

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