Originally Posted by powertrip
Good points, BUT I will most certainly disagree with your thoughts of OTS map vs a custom tuned map. My OTS map was actually making less HP than the stock tune. Why? Because the tuner had manipulated the throttle openings on top-end. End result, the car felt great until 7000 rpms where it began to close the throttle. My custom tune is head and shoulders above that ridiculous attempt at a tune
This sounds to me like a problem with the OTS map rather than something specific to your car that required a "custom" tune to resolve.
Honestly the only custom tuning that is going to make any difference is tuning VANOS based upon your modifications (specifically around intake and exhaust). But this is something that is exceedingly complex to manually tune and could only be done quickly and efficiently by being about to model your specific engine/intake/exhaust configuration (i.e. expensive computer software that BMW spends $$$$ on)
Note that there are some tuners who are starting to play with VANOS and are getting impressive power gains (like double what is currently achieved) with OTS tunes. Hopefully I'll have such a tune soon once some issues with my car are sorted out