Originally Posted by
buffordboy23
Yes, you are right in some regards. Here is a more precise description. At stoichiometric, a large amount of heat is available during combustion, however, not all of the gasoline is combusted. Therefore, if we run leaner, then this extra portion of gasoline is more likely to be combusted, giving off more heat energy than before, so this could result in the scenario which you describe. If we lean the engine out even more, so that the extra air has negligible effect on combusting this extra gasoline, then the role of this extra air is to absorb more heat from combustion so that gases do more work on the piston, and less heat is transferred to cylinder walls. This increases the thermal efficiency of the engine, and is why many people lean their cars to for hydrogen addition.