Whether you have mods or not I thought that the computer would compensate and adjust the air/fuel mixture on its own.


[Modified by vettvert, 12:09 AM 8/10/2001]

 

A good question, not asked often enough.

The purpose of installing larger MAF ends is 1) having the capability to flow more air and 2) to potentially increase timing.

The first, increased airflow, is only realized in situations where the engine has been modified such that it pumps more air. The stock MAF assembly is completely adequate in this respect for stock displacement naturally aspirated emgines. Larger ends do not "flow more air" they are merely capable of doing so.

The second, increases in timing, relies on your observation that AFR is maintained by the PCM at part throttle. Using larger ends with a stock sensor results in reduced air speed across the sensor. Due to the design of the sensor, the PCM perceives the resulting signal as indicating less load and is more likely to pick more aggressive timing as a result. A side effect of this is that less fuel is also delivered. This is quickly compensated for as the O2 sensors detect the lean condition (caused by a decrease in fuel delivery, NOT an increase in air) to which the PCM responds by lengthening injector pulse width.

The problem is at WOT where the O2 sensors are not used. This is where things like adjustable fuel pressure regulators, larger injectors, MAF translators, "5% rich Granatellis", Halltech magic boxes and the like come into play.

The AFR conditions are a side effect of trying to achieve timing gains by exploiting the design characteristics of the MAF sensor with larger MAF ends. It should not be surprising that most tuners who address timing via PCM programming prefer the stock ends.

HTH.