This may be the wrong forum, so mods please move if necessary (and forgive my error :) ). I was trying to research combustion temperatures (for a typical four stroke engine) as they relate to air/fuel ratio (AFR). I have googled my butt off, and I read many interesting things. But, I still have some questions. My wisdom (or lack thereof) and experience tell me that leaning an AFR from stoichiometric, 14.7:1 (A/F), will cause exhaust gas temperatures (EGT) to decrease. The result being due to the fact that more of the heat is being absorbed in the combustion chamber primarily due to less fuel being available for both 'cooling' and controlled burning. In fact, if one see rising cylinder temperatures and decreasing EGT's it is a sure sign of some other form of ignition (detonation or pre-ignition) in the cylinder. It is also true in my experience that EGT rises when the AFR is made richer. I have always assumed that this was because some of the fuel was 'cooling' (absorbing heat) the mixture, and much of that was carried out through the exhaust stream and dissipated through the exhaust system. A good example of this is turbocharged engines. They need to run much richer than 14.7:1 in high-load situations, and their EGT's are much higher. What I am curious about is any information describing actual combustion temperatures related to different AFR's. If the combustion process is complete (or successful) is there any difference in combustion temperature when the AFR is say 11.5:1 versus 15.5:1? I am guessing that an engine would make more power with and AFR of 15.5:1, but that it could only do it once because the heat would not be tolerated by the components. Older racers, always thought that leaning out the AFR made EGT's rise. I think this is because cars used to come from the factory with much richer AFR's, and when they leaned them out EGT's actually rose some. However, I have never experienced this (and I am not that old), so I am a little confused. More Power = More Heat. At some point though, a really lean mixture say 20.0:1 isn't going to burn very well. So, I assume at that point there is less heat. Is there a curve plotting heat versus AFR? Sorry for the long rambling post.