I wanted to move this out of my build thread since that's coming to a conclusion and post up this info here for some reading material...
I've run the AFRs on the stock engine and here's the main event in a quick rundown But first a lesson on what the AFR readings mean...
A “stoichiometric” AFR has the correct amount of air and fuel to produce a chemically complete combustion event. By definition, stoichiometric is the calculation of relative quantities of reactants and products in chemical reactions. Which is a fancy way of saying it’s a mathematically derived “ideal” ratio of air to fuel. For gasoline engines, the stoichiometric AFR is 14.7:1, which means 14.7 parts of air to one part of fuel.
The stoichiometric AFR depends on fuel type—for alcohol it is 6.4:1 and 14.5:1 for diesel. For the purposes of our conversation here, we’re just concerned with a gas-burning engine, so 14.7:1 is the ratio that lies in the middle of a “rich” or “lean” mixture. A lower AFR number contains less air than the 14.7:1 stoichiometric AFR, therefore it is a richer mixture. Conversely, a higher AFR number contains more air and therefore it is a leaner mixture.
For Example:
16.0:1 = Lean
14.7:1 = Stoichiometric
12.0:1 = Rich
.
Leaner AFR creates higher temperatures as the mixture burns. Generally, normally aspirated spark-ignition gasoline engines produce maximum power just slightly rich of stoichiometric. In practice it is usually kept between 12:1 and 13:1 in order to keep exhaust gas temperatures in check and to account for differences in fuel quality. A 12:1 AFR is generally considered to be about right on a gas engine under full load (wide open throttle, hooked up and haulin’ butt), though there are certainly exceptions depending on a million different things.
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