| What you are seeing with a leaner mixture is the result of some other variable. It is not running leaner because the system is moving more air. Our EFI systems are mass-airflow based. This means that the sensor that is employed is measuring the mass of air passing through it. We know the composition of atmospheric air and based on a total mass measurement, we can determine how much oxygen is being consumed by the engine. With this information, the quantity of fuel necessary to produce a stoichiometric mixture can be easily calculated. This is exactly what our ECUs do. Now in the case where you alter the system in such a way that the air mass entering the engine is changed, the sensor will still measure the mass of air entering the engine and the ECU will use this to determine fuel delivery. If more air is coming in, it sees it, and will add more fuel as well. On top of that, the general trend in fuel maps is to increase enrichment as load increases. So not only will the ECU add more fuel solely to match the additional air coming in by way of some performance mod, but it will also add an increasing additional enrichment value to it as the load increases. If you are seeing leaner mixtures after a turbo inlet pipe install, there is something else going on. I would expect to see small changes, but that would be towards the richer end of the spectrum, not to the leaner.
Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the
tailor.
Albert Einstein
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