First, a little piece of basics. Due to the nature of things there's an air-fuel ratio that is supposed to be correct for total combustion. This is the 14.7:1 air:fuel ratio. Of course it isn't the best for either power or mpg. It is usual to refer to certain lambda values, i.e., 14.7:1 corresponds to lambda=1 and (14.7*0.9):1 is lambda=0.9. For the best power lambda=0.88 is feasible and lambda=1.1 for mpg.

There's probably only one certain way of knowing what the mixture actually is. An device called the lambda-sensor is fitted to most cat-cars and is a good measurement point to declare the actual micture. As it only works when hot enough, a heated type is preferred for better accuracy. Lucky for us, the mixtures aren't ultra-sensitive, I've made some measurements.

The best power should be at ~.88 lambda that should be somewhere around 910 mv with a 1Meg DVM. This curve probably represents 10KOhm VM.

Back to catalog