The EEC has a mass air flow transfer function (it is nothing like the ones from Pro-M, the EEC values are in lbm/clock tick, don't ask why, I don't know) of voltage vrs flow. The EEC also knows the engine size and RPM. Knowing air flow, engine displacement and engine speed, you can calculate the volumetric efficiency of the engine. (voleff is the amount of air flowing into an engine divided by the total possible air, or engine displacement). For a naturally aspirated vehicle this number is almost always less than 100%, and for the vehicles were talking about it is.

The EEC looks up spark and a/f ratio based on engine speed and voleff. The higher the engine speed at the same voleff, the more spark. The higher the voleff at the same engine speed, less spark.

When you modify the sample tube in the MAF, you essentially lie to the eec and tell it it has less air flowing into the engine than it really does have. So it picks the fuel and spark curves from a lower voleff point. Usually this means more spark and less fuel. To a point this means more power. If you go too far, it will detonate.

Now lets get to Pro-M. In theory, and Dan Ulrich will attest this is not true based on his post below, but in theory, they know the original air meter transfer function, and can then make you a new unit with the same transfer function and all is well. But, even if they start with same curve, they will tend to skew the curve. This is what they call 5% rich, 10% rich etc. What this does is then lies to the eec again and makes it think that there is really more airflow than what there is. I think they do this so people don't run their engines lean and make them go boom. I feel they shouldn't do this, and I'll explain.

From the factory most engines are calibrated to run rich for two things, exhaust valve temperature to a lesser degree, and mainly to keep the catalysts cool so they don't burn up. Most of your T-Birds run about 11:1 A/F at wot, skew the curve 5% richer and that makes the engine 10.4:1 a/f ratio. The richen up supercharged air meters even more.

The right way to install a Pro-M airmeter, but a costly way, is this. Get the data from your air meter, which they supply you, and then put this data in a regression program to come up with an equation of voltage vrs air flow. Then come up with 29 points between 0 and 5 volts and have the eec changed to reflect this transfer function. I don't know of anyone that does this, not even the best "tuners".

What "tuners" do is this. Ask Pro-M for a air meter, and this is just an example, that started as a 19 lb Mustang but is "re-curved" for 38# injectors. What Pro-M does is make an air meter with a transfer function that at their two flow points has double the air flow of the stock air meter (38/19=2). Then they run their 10 point curve. The "tuner" then installs this air meter with 38# injectors. But if you go up top the EEC calculated voleff. This is now off. So the tuner then lies to EEC some more and says the engine is 1/2 the displacement it really is. This does make the voleff calculation correct. The problem is Pro-M only has two points that they can adjust on their curve and you take what you get. If you look at the data sheets there is sometimes alot of error at the high flows, I've seen as much as 20%. The right way is to put the full 29 point curve into the EEC.

Even though the autologic software has the ability to put in all 29 points, I've never seen anyone that does this.

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