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As a quick reference, here are lambda values and their AFR equivalents for different fuels. This is handy to use when looking at a wideband display/gauge that displays a gas scale AFR or just for curiosity’s sake.
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Gasoline Desired Eq Lambda E85 Ethanol Methanol 8.00 1.84 0.54 5.32 4.90 3.49 8.25 1.78 0.56 5.49 5.06 3.60 8.50 1.73 0.58 5.65 5.21 3.71 8.75 1.68 0.60 5.82 5.36 3.81 9.00 1.63 0.61 5.98 5.52 3.92 9.25 1.59 0.63 6.15 5.67 4.03 9.50 1.55 0.65 6.32 5.82 4.14 ... Air Fuel Ratio Conversion Chart.
E85 Ethanol Diesel Methanol Natural Gas Propane 14.7 : 1 9.8 : 1 9.0 : 1 14.5 : 1 6.4 : 1 17.2 : 1 15.7 : 1-----Stoichiometric AFR of Common Fuels AFR - Lambda Lambda - AFR 0 50 100 150 200 250 300 0 1000 2000 3000 4000 5000 6000 7000 8000 DEAD 0.95 - 0.90 DEAD
So to be more specific, E85 and pump gas tend to work well at very similar lambda targets. For this reason you can (and most tuners do) just leave the wideband stoich setting at 14.7:1 (correct for pump gas), and tune for the same targets you'd use on pump gas.
1 kwi 2022 · Building a proper E85 fuel system will take advantage of all the performance benefits of pump E85 while mitigating the risks. Flow capacity, material compatibility, tuning, and maintenance are the biggest considerations.
Personally, I've always found 12.0:1 on E85 (pump gas scale) gives you plenty of cushion to play with the tune, while making good power overall. But here again, each application is different, and the tune (to include AFR) needs to be specifically tailored to the individual setup.
The table below shows the requirements of the ASTM D5798 Standard Specification for Ethanol Fuel Blends for Flexible-Fuel Automotive Spark-Ignition Engines. ASTM regularly updates standards, and the latest version of the specification is available on the ASTM International website.
