When To Recalibrate The ECM

This question comes up often...

Whenever the amount of air or how the motor processes it is changed! Period!!!
The major components influencing air flow are the exhaust system, air cleaner, motor size, heads and cams. If any of these are changed, the fuel (via the VE and AFR tables) and, typically, the tuning constants table in the ECM must change to match (synchronize) both the increases and decreases in air flow and physical characteristics of the motor caused by those component changes.
On “closed loop” models, the above is true when the changes exceed the O2’s capability to compensate, to reduce the amount of correction required of the O2's or to change tuning constants (motor size, injector size, etc).
In addition, there are certain “behind the scenes” tables that have strategies to add fuel for extended high rpm running or heat management, retard timing for knock control or heat management, injector off timing to reduce decal pop, change VE values (O2 equipped models ) or even to deal with high rpm down shifts in efforts to prevent engine damage or reduce ECM workload in extreme cases.
Even with Race Tuner, we normally do not have access to these tables and cannot change them. These strategies/tables may be different from calibration to calibration and so, having the most appropriate base calibration helps these to be closer to, or more correct, for the application.