The ECU must be working inside some really tight set parameters do be able to do this!
Most modern ECU's are to some degree adaptive but this sounds like something taken to a different level.
Even by passing this ECU learning factor, I'm well aware that an engine has a limit as to what kind of power it can produce. The Z may already be near this limit as it is and therefore modifcations to the headers, intake will really only change the power delivery rather than increase the output.
If modifications aren;t working that well it simply means everything has been pretty well designed from factory and the Z is a well optimised.
With approx 80 BHP per litre out the box it is quite highly tuned to start with.
In which case - you guys are spot on, these mods are about increasing the driveability rather than out and out power.
If i'm wrong in anything I say please correct me.
A