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Normal e10 mix got me 19 mpg. E85 I averaged 13 mpg.....More used fuel is more carbon, that's what " they" are worried about, right?
Thats not completely true. Yes, burning more fuel releases more carbon to the air. But if you burn 100% ethanol that carbon came from corn or soy beans which removed that amount of carbon from the air as the plant grew. So you are effectively recycling the same carbon.
Gas, diesel and natural gas are all oil based which releases new or additional carbon to the air that was previously stored underground for millions of years.
So thats the main difference, adding new oil carbon versus recycling plant carbon.
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On a different topic in this thread. I think there is some confusion on exactly how a wideband O2 meter works. The sensor is reading Lambda of the exhaust gas and the gauge converts it to AFR based on how it was programmed. Stoichiometric for gas is 1.0 Lambda, stoich for E85 is 1.0 Lambda.
Yes, your ECU needs to know how much fuel to put in based on the fuel being used but the wideband is just measuring the results. If we all used Lambda like we should, the gauge would be accurate for all fuels. If the gauge is programmed such that 1.0 Lambda equals 14.7 on the display, then that is what it will display even if you are running E85. The gauge doesn't know what fuel you're burning. For example, if the sensor measures 0.8 Lambda (rich), then it will display 11.8 regardless if its gas or ethanol.
Maybe this is a better explanation
https://www.motortrend.com/how-to/wideband-oxygen-sensor/
The world won't end or be saved with E15 just like it didn't end when lead was removed. People just hate being told what to do and that they need to do it because its good for them.