I'm trying to figure out where the often cited 14.7:1 stoich a/f ratio for gasoline comes from. I've always thought it was calculated from a primary reference fuel containing some mixture of iso-octane and n-heptane. But I've done the calculations for those hydrocarbons and my numbers don't match up. I did some figuring in THIS THREAD. I did the math again with less rounding and I'm getting: iso-octane: 15.03:1 n-heptane: 15.08:1 I'm trying to tweak my calculations (concerning how to figure in the atmosphere that is NOT oxygen) to see if that is my problem. If nothing comes of that.... My question is, were is 14.7:1 coming from? Which hydrocarbons and in what mix are "they" using to come up with that figure? And what composition of air would be used? Does anyone know? note: I'm not looking to figure any real-world situation. Rather, I'm concerned with how the 14.7:1 figure is generated.