[RustyLugNut]

The subject is a complex one and that is why there is seemingly contradictory information.

One area of misunderstanding is the area just lean of stoich or 15-18:1 air fuel ratio (AFR). Someone had already posted a graph on another thread showing the classic increase in combustion temperature in this lean combustion mixture. It goes against logic that combustion temperature would increase when there is an obvious reduction in fuel. But, we must not forget that N2 is present and will oxidize given enough endothermic energy and will then release energy adding to the combustion heat.

Beyond 18:1 AFR, the heat capacity of the lean mixture reduces the formation of NOx.

The above is not to be confused by the "racer speak" of "lean mixtures". Racers run their gasoline engines about 12:1 AFR to provide extra fuel to cool combustion via extra heat capacity and thermochemical formation of CO and HC. Running "lean" could still mean 13-14:1 AFR and detonation conditions occurring.

Running lean beyond 18:1 AFR will result in reduced heat and pressure output until the limits of flammability are reached.

Also, most high performance testing is done at wide open throttle and maximum heat production.