BimmerRob08,
It's like J08M3 said.
MAP sensor (Manifold Absolute Pressure)
MAF sensor (Mass AirFlow)
The S65 V8 M3 uses a MAP sensor.
If you wanna learn more on these sensors readup on them on Wikipedia.
http://en.wikipedia.org/wiki/MAP_sensor
http://en.wikipedia.org/wiki/Mass_flow_sensor
Map sensors don't see changes in engine volumetric efficiency as well as MAF.
Since BMW tuned the DME according to it's factory tested % of engine volumetric efficiency, with required values to make there performance requirements.
Now adding a few extra % of volumetric efficiency on a engine from a exhaust and air filter. The DME doesn't see them as well with a MAP sensor and cannot adjust the fuel for
optimum performance.
But the engine has safeties built in so you don't damage the motor from leaning out.
By using the integrated 8 knock sensors and 4 O2 sensors.
Now this is what i know, but i don't know all the DME functions and tune. As i'm no tuner.
Maybe tuners on here will clear some of this up.