i don't beleive physical size is what dictates overall hp rating, i think it has to do with how much the sensor can vary in resistance.


Hot wire sensor (MAF)

A hot wire mass airflow sensor determines the mass of air flowing into the engine’s air intake system. The theory of operation of the hot wire mass airflow sensor is similar to that of the hot wire anemometer (which determines air velocity). The General Motors division (GM) was the first car company to use the hot wire sensor.[citation needed] This is achieved by heating a wire with an electric current that is suspended in the engine’s air stream, like a toaster wire. The wire's electrical resistance increases as the wire’s temperature increases, which limits electrical current flowing through the circuit. When air flows past the wire, the wire cools, decreasing its resistance, which in turn allows more current to flow through the circuit. As more current flows, the wire’s temperature increases until the resistance reaches equilibrium again. The amount of current required to maintain the wire’s temperature is directly proportional to the mass of air flowing past the wire. The integrated electronic circuit converts the measurement of current into a voltage signal which is sent to the ECU.

If air density increases due to pressure increase or temperature drop, but the air volume remains constant, the denser air will remove more heat from the wire indicating a higher mass airflow. Unlike the vane meter's paddle sensing element, the hot wire responds directly to air density. This sensor's capabilities are well suited to support the gasoline combustion process which fundamentally responds to air mass, not air volume. (See stoichiometry.)

Some of the benefits of a hot-wire MAF compared to the older style vane meter are:

* responds very quickly to changes in air flow
* low airflow restriction
* smaller overall package
* less sensitive to mounting location and orientation
* no moving parts improve its durability
* less expensive
* separate temperature and pressure sensors are not required (to determine air mass)