You still want to shoot for richer A/F ratios than you'd normally use on your car, and use the cooler air charge to allow you to increase timing. You're shooting for a lambda value of under .8 for pure gas if your wideband can display in lambda, because that's actually what the sensor reads (and translates to a/f). Meth doesn't have as much margin for lambda, so shoot for .78 or less.