Mass air flow

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Mass air flow

The term in its simplest form means mass (in grams, pounds, kilograms, etc) flowing through the engine or past a metering system over a period of time. Typical units include grams per second (g/s) and pounds per minute (lbs/min). Grams per second appears most often while tuning. Turbocharger compressor maps are most often in lbs/min. These are still compatible units of measure and can be directly converted and compared using simple math.

Mass air flow can also be used to describe a tuning methodology, similar to speed density or alpha-n.


In mass air flow metered engines, the air flow meter provides a voltage to the ECU. The ECU translates this voltage to mass air flow using a flow scaling table. This total mass flow over time can be further divided to a load value, which represents the mass of air that flows through a cylinder per crank cycle (or every other crank cycle, etc). The actual load value is typically used as a reference for numerous other tables, but most notably ignition timing and fuel enrichment tables.


Mass air flow systems have the advantage of consistency over a range of environmental conditions and speed. The sensor itself produces a consistent voltage output for the mass of air flow irregardless of air temperature, humidity, barometric pressure, coolant temperature, cylinder head temperature, and volume flow. While not perfect, far less compensation is needed for these other environmental factors compared to alternatives.


Mass air flow systems require a sensor be placed somewhere in the intake tract which impedes airflow. Often factory car's mass air flow sensors will max out with high output turbos, engines, or tunes, as the factory car never intended to flow the higher levels of air. This may require a larger diameter mass airflow sensor body or an aftermarket or modified sensor.

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