%20-25 long term fuel trim and %20-25 short term fuel trim ... it can only apply these adjustments to bring the idle and part throttle conditions to a 14.7 stoich burn. the final numbers are still applied to wide open throttle conditions but do not adjust based on wide open throttle air fuel ratio as the narrowband sensor is only accurate at 14.7...

and yes it would be possible to reprogram the ECU but at too high a cost and each build would have to be tuned as variances in what turbo was used or intercooler would affect tune required .... so unless a company makes a kit and has ECU's mass reprogrammed to be distributed with the kits then the cost would be very high. hell its going to be high no matter what you do for these cars ... so yes its all possible, how fat is your wallet ? how bad do you want it ?