How much will the stock ECU adjust the fuel map with intake/headers/exhaust

[mikstew]

My two and a half litres of displacement are beginning to feel puny. I want some more ponies, so I am thinking of opening up the intake and exhaust on the car.

With a new filter, cold air box, headers and exhaust (cat-delete), I am hoping to achieve my goals.

However, doing these mods will not yield any benefits unless the ECU adjusts the A:F ratio appropriately. How much can the ECU do? +/-5%? 10%? 25%?

And with that adjustment, how much power % increase would come with the mods?

From what I know, the ECU makes adjustments based on the pre-cat O2 sensor reading, which would not be affected by deleting the cats.

I plan to prevent a CEL by installing a spark plug fouler (defouler) on the post-cat O2 sensors.