Most of the information I have tried to contribute to this discussion thus far has been based on fact. However, I have a question/idea. Think of the density differnece between air at a high elevation on a hot humid day v/s the air at sea level on a cool non-humid day. If the ECM can correct for such a big difference in air then in theory or at least in my mind it could easily accomodate for a mild shot of N2O (say maybe 50hp) flowing past the MAF sensor. I'd like to see some sort of calculation based on the amount of oxygen at elevation, sea level, and with a mild shot of N2O. I wonder if there really is that much of a difference. I hope what I am trying to say makes sense???
Yes, you are onto the right track. I have been tuning LT1's, LS1's, and BBC's for a while now, but admittedly I am fairly new to the mod motors and Ford PCM's. But so far from what I can tell, the GM and Ford PCM's are not all that different.
Here is my personal experience so far with these mod motors.
One of the things the PCM does to adjust fueling is calculate how far off current air density is from the VE tables referenced density. To determine the density of the atmospheric air, it is necessary to know is the actual air pressure (absolute pressure), the water vapor pressure, and the temperature. Since our cars don't actually have a baro sensor or MAP sensor, our PCM's don't have a way to finitely determine what altitude we are at nor what the outside absolute barometric pressure is. It has to make an educated guess using known gas constants and data sampled from the MAF and IAT collectively.
Here is something that seems to confuse a lot of people even tuners. A molecule of 100% relatively dry atmospheric air contains more mass than a molecule of pure water. So it is important to consider the individual mass of each of the molecules in the airstream flowing through the MAF. Nitrogen comprises about 78% of the air our motor’s inhaled air, and Oxygen comprises about 21%. Then there is less than 1% of other trace elements. Nitrogen has an approximate atomic weight of 14, so an N2 molecule has a overall weight of 28. Oxygen has an approximate atomic weight of 16, so an O2 molecule has a weight of 32. Then we have a water molecule, or H2O. Hydrogen has an atomic weight of 1. So the molecule H20 has a weight of 18. Notice that a H20 molecule is lighter weight than either a N2 molecule or an O2 molecule. Therefore, when a given volume of air, which contains only a certain number of molecules, contains some relatively light H20 molecules which in turn prove to yield less mass, it will weigh less than the same volume of air without any water molecules.
When humidity increases, and altitude and temperature remain constant, relative air density decreases. Humid air, with a relative humidity of 100%, contains about 0.023 kg of water per cubic meter of atmosphere. That makes up less than 1.9% of the mass passing by the MAF. The MAF doesn't care what is traversing the MAF sensor elements; it can be N2 molecules, O2 molecules, H20 molecules, etc.. It's all mass to the MAF, but the different types of mass effect the MAF sensor element cooling in different ways so that is important to bear in mind. Since the dry air molecules actually contain much more mass like I mentioned above, they have much more of an effect on the cooling effect on the MAF sensor elements than does the humidity (H20) in the air. Neither the MAF sensor nor the PCM know what is cooling the sensor element, they make an assumption based on the voltage required that is sent in return to the MAF to maintain a closely monitored target voltage through the sensor. This assumption is reflected in the Frequency(Hz) to Airflow(g/sec) lookup table. So humidity has the least effect on air density as compared to changes in altitude (Baro) and temperature.
View attachment 416887
Ideal Gas Law - P*V = n*R*T
P = pressure
V = volume
n = number of moles
R = gas constant
T = temperature
Suffice it to say, there are some fairly complex thermodynamic algorithms that go on within our PCM's that most people are completely unaware of. The BARO PID (Parameter Identification Display) and the fuel trims (mainly LTFT’s) are closely related. Humidity has more of an effect on STFT’s.
Another thing about the MAF sensor is that it is not an airflow meter like an anemometer. It is only good at determining changes in mass airflow and it always assumes a laminar flow, that is it assumes that the air that is passing through the sample tube or over the elements is wholly representative of all the air passing through the entire MAF housing. The MAF and PCM are also hardwired to assume that the air flow will be inconsistently unidirectional.
