How far is too far, how lean is too lean? On full e85, have lean cruise about 15.5 - 16, is there any potential issues with pushing it until driveability is a concern? Also any advice on what afr to target under light throttle or hard throttle below 100kpa?

 

No fuel savings advantage going past ~15.4 relative gasoline scale. Beyond this ratio power reduces and the operator is forced to increase engine load (throttle) resulting in the same equivalent fuel usage.

Edit: there is a fractional advantage to accessing superior VE with greater throttle angles at a cost of dynamic range. Driving behavior is dramatically more effective at improving gas mileage.