Your wideband O2 is reading lambda and then translating that to an a/f number setup for the fuel the O2 unit was intended to be used with.
14.64 to one for gasoline = 1.0 lambda.
6.45 to one for alcohol = 1.0 lambda.
.72 (lambda) x 14.64 (stoich a/f for gasoline) = 10.54 to one. The simularities? Pretty rich for gasoline.
.72 (lambda) x 6.45 (stoich for methanol) = 4.64 to one. The simularities? Pretty rich for alcohol.
You could switch completely over to alcohol and your O2 would read the same. The a/f numbers that you may want to target may change because of the different characteristics of the fuels, but the sensor readout numbers will be similar to what you'd expect to see as if you were running gasoline.
Some people get used to tuning using straight lambda numbers without translating it to an a/f number for the particular fuel being used. In that case, they're aware of what lambda number works for each type of fuel and that lambda number will be very close to being the same from fuel to fuel.
1.0 lambda is stoich no matter what fuel you're using. Gas to propane to nitro.
.72 is a safe WOT rich mixture. No matter what fuel you're using or what percentages of fuel mix you're using.
.91 lambda is a lean best WOT mixture. No matter the fuel or mix.
Now the target lambda (translated to a/f number) may be slightly different when changing or mixing fuels because of the changes in the properties of the fuels, but you will find that the O2 reading will end up staying with what you're already familiar with. A/f readout numbers on a gasoline fuel scale.
Just remember the sensor reads lambda. Then translates that number to a number that you can be more familiar with. A/F ratio. When you start mixing or changing types of fuels, just keep reading the sensor as if you were still on straight gasoline. Keep in mind though, that with the new fuel or mix of fuels, the fuel properties has changed from that of straight gasoline and new target a/f numbers may be necessary. Still the numbers will not be drastically off what you'd expect with straight gasoline and the new numbers will not be a true indication of the ACTUAL new a/f ratio you'll be running.
For instance, my target rich WOT a/f number is 10.5 to 10.7 to one for 24 psi boost. Very close to what everyone here has been recommending. That is what I have programmed into my ECM and that's what reads out in my datalogs. As I start moving up into higher boost, I'm sure I'll be moving that target to somewhere closer to 10.2 to 10.3 to one to make more use of the chemical intercooling properties of the methanol.
Every engine combination is different. The target a/f number from one combination may be wrong for yours. The only safe way to do this is to start out rich and move to lean until you've found the best performance without getting into detonation or worse.
By the way, my engine runs on pure methanol only.
