14.7 to 1 is considered the stoichiometric air/fuel mixture. Anything more than that is considered lean and any thing less is considered rich. Lean can be very dangerous because it causes the engine to run hotter. Way hotter. Hotter such that internal parts can warp and melt. Gas is not just used for the "bang" but also for cooling the combustion chamber. Oxygenated fuels can lower the a/f ratio to somewhere around 14.1 to 1 but as you see it is only very marginal. On more modern engines with special alloys and coatings I can see that the ratio could be leaned out a tad.
1994 Wrangler YJ
31x10.5x15 BFG MT