Originally Posted by Artifex

Not true.

The AEM has several features which OBD1 derived S/W does not. I know because I've tuned Uberdata, Crome, and the AEM personally on my own car. These are:

(1) Gear dependant wastegate maps (Neptune has this also). Allows different boost targets for each gear (traction).

(2) Direct fire ignition drive for COP. OBD1 can't do this. COP yeilds very nice improvements at the very top end.

(3) Battery voltage compensation. Sounds silly, but at high loads, the car's supply voltage will drop slightly. The AEM measures the voltage, and compensates the fuel injector duty cycles.

(4) Fuel injector offset timing. This one is the hotness. The AEM has a 2D map which is an offset (in ms I believe) from when TDC is reached (used repetedly for each cylinder). It delays the fuel injector open time until the offset has passed. This allows the fuel to be sprayed only when the intake valve is actually open (at low loads). At high loads, there isn't much tweaking room. User JDogg is an expert AEM tuner, and he has picked up as much as 10% power in the midrange by tuning this parameter. Also, it helps tremendously at idling large injectors, and low-throttle fuel economy.

Granted, you need a tuner that can tune all this. I have a low opinion of any AEM tuner who can't, since I was able to do this myself. It requires a few hours street tuning, and a few more at WOT on the dyno.