Open loop is open loop........meaning it runs on the map with no adjustments, no learn. It reads the 02 of course, but makes no changes based on the info.

With aftermarket EFI, you can turn on closed loop whenever you want, based on the parameters you program it to recognize. On our own car, which leaves at 3400 on the brake, I delay the closed loop until 5000 when on the race tune. This keeps the 02 from "chasing" and trying to correct on the brake, plus lets the motor accelerate clean OFF the brake. Of course it reaches 5000 quickly, but the car is already moving well at that point. Others might need this number higher or lower, depending on converter. Ours is REALLY tight

Monte