[twobjshelbys]

The perfect AFR is 14.7:1. 15.0 would be lean, 14 would be rich. The problem is that where you measure makes all the difference in the world, and so an O2 sensor measurement taken in a Cobra side pipe by a sniffer cannot be taken as absolute. You can use it to se how much you are changing things though.

P.S. I got to know way more about this than I needed or wanted to when I was trying to get my Accel DFI system working. As an engineer it was an interesting exercise. Now I just either use new cars with really good computers (like the Ford GT) or tune the carb until it sounds right (like my grandpa taught me).