Introduction
Like carburetors were in the 60's and 70's, mass air meters are today one of the "bigger must be better" modifications that performance seekers ponder over.

If you own a mass-air 5.0L vehicle, then you are no doubt aware of all the hype surrounding bigger mass air meters and throttle bodies. The stock mass air meter is restrictive, so they say, and you must upgrade to larger bore to allow the engine to breathe -as the argument goes.

Typically such arguments rarely apply to stock or relatively stock vehicles. Sure, a 5.0L with better heads and maybe cam will need to reduce the upstream restrictions, but is there really anything to gain by doing this on a stock engine?

We decided to find out. We obtained C&L's new 76mm mass air meter and "Trueflow" tube package and tried it on a pair of vehicles. We installed it first on a bone stock AOD 5.0L Mustang, replacing the stock 55mm unit, and track tested it. Then we installed it on a modified 5.0L engine, along with some matching 24lb injectors, and compared the results to the stock 19lb meter/injector combination.

Hot Wire Anemometry

First, an explanation of mass air meter operation. The mass air meter sits in the intake tract, between the air-filter and throttle body. On 5.0L engines it is typically found close to the passenger side shock tower and fender.

The mass air sensor's purpose is to assess engine load by measuring the quantity of air coming into the engine. The EEC uses inputs from the mass air meter to tailor air-fuel ratio by altering fuel injector pulse width -the amount of time the fuel injectors are opened. All 5.0 liter Mustangs with mass-air use a dual wire sensor element attached to a cast-aluminum meter housing. Other types of mass air meters use hot-film elements, which we won't get into here.

The sensor element is comprised of two wires, made from platinum or tungsten. One of the wires is a sensor, and references ambient temperature (the temperature of the incoming air.) The second wire is a heater, and maintained at a temperature of about 212 C. over the ambient air temperature. As air speed over the elements increases and cools the wires, a correspondingly larger electric current is required to keep the heated element at 212 deg. over the sensor element. Voltage output corresponds to a change in airflow, from 0.5V to 4.5V. The sensor itself is not located in the main stream of airflow, but in a smaller side channel known as a sample tube.

Air flowing through the smaller sample tube is proportional to air flowing through the main body of the meter Thus, the entire amount of air passing through the meter can be accurately sampled without causing damage to the sensor element or undue restriction to the incoming air.

Because the cooling effect of the moving air is directly related to the temperature, density, and humidity of the air, the current change is proportional to the "mass" of the air entering the engine. The advantage of using a mass air meter metering over speed density is that regardless of production differences in volumetric efficiency between engines, the air/fuel relationship may be reasonably maintained as constant. From a performance standpoint, relatively large improvements to volumetric efficiency can be made without reprogramming the EEC control module.