Following the results of a recent Dyno day we are convinced the Unichip gets overridden by the ECU over time and requires a retune regularly to maintin peak performance. Nikich, the ECU does learn when you add mods, resetting the ECU just hurrys up the process. The ECU sets it ideal A/F maps by averaging data over a period of time. If you don't reset the ECU that time is longer so the time to perform the average with the new bits takes a longer time. Resetting the ECU gets the base average done in 1/2 an hour of driving. As Rollamods said there are changes to the timing too, but with breathing mods like a CAI and exhaust the A/F ratio is the most important thing.