Just my .02
Get a standalone system like wazzu70 mentioned. You will have complete control over your engine. Here is a synopsis from our M3 list back in the day.
Enjoy...
Cheers,
~Ralph
Alpha N, first of all from a terminology perspective, came from the mathematical representation of the Greek symbol, alpha, to mean throttle angle and N to denote RPM. Engineers used these letters to represent the equations of this system and hence the name.
When you look at reasonably modern engine management system (ok, just pick something understandable like Ford EEC-IV or Bosch Motronic), there are many inputs that go into fine monitoring of engine variables to ultimately do two things:
1) control fuel injection pulse width
2) timing advance
Generally speaking, as you have more closed loop information and control, you have more ability to deal with variance. If you know exactly how much air is really coming into the motor in volume and you know what the exhaust byproduct looks like, you can use that information to alter fuel delivery and ignition timing. So yeah, you can actually drop a cam in a car with a good engine management system and have it run within reasonable (though not optimal) power ranges.
Why not optimal? Because, at least both engine management systems I mention above, bypass things such as O2 sensor input when running at WOT (Wide Open Throttle). At WOT, the engine uses maps in the ROM (read only memory) to give predetermined timing and fuel. Once your cam has changed (and obviously I'm just using a cam as an example), its profile may be better suited for a different predetermined set of WOT timing and fuel values.
So what is Alpha N for and why would you want it? Well frankly, its use is rather limited. Alpha-N provides no intake limitations (restrictions) since no air is measured beyond the inherent throttle angle. If you are running a race motor with a high lift, fast rising cam, you want all the air velocity you can get and that means as little restriction as possible. Motors like these, frankly, idle like shit.... they make no sense on the street. Recall that modern engine management systems gave us great low RPM performance (for those of you old enough to have owned carburetor cars) because of the ability to closely monitor sensors and determine close to optimal timing and fuel injection pulse width. You don't get that with Alpha N ... hence another street detriment.
Why is Alpha N so intolerant of engine configuration changes, or environment changes? Because its approximation of real air volume (just using the throttle angle and maybe barometric pressure and air temperature) no interest in exhaust measurement (closed loop) and not much else, it runs off of a table which effectively is indexed by throttle position versus RPM with possible compensations from barometric pressure and intake temperature. How do you build the maps? Simple ... spend hours on the dyno with expensive EGT sensors and develop the specific maps for the specific engine configuration until you get it optimal or give up and say it is good enough. Now you have a completely static system highly tuned to its configuration. Change anything and it's a no go. Even something like the exhaust system...
