Another of those things I occaision come across on the net....I never have any financial interest in these things btw...
http://www.sol2.be/Performance/ENG/Theory/page.html

The article is a joke, you must use wide band O2 and not a narrow band Lambda sensor for closed loop control

PC5 with autotune is the way to go, it is full time all the time closed loop control with wide band O2 sensor

wide band 02 closed loop control:

In simple terms, closed loop control takes air/fuel ratio measurements form the exhaust mounted Bosch wide band sensor (very high rate highly accurate), this data is analyzed by the PC5/auto tune and adjust the fuel delivery to the injectors real time all the time based on the air/fuel ratio you select in the PC5....

narrow band lambda sensors do NOT have the sample rate and accuracy to gather data fast enough to feed back changes to air/fuel in real time

I run 13:1 AFR

turbo or supercharged motors need 12 to 12.5:1 AFR for gasoline, alcohol motors run 6:1 AFR

this guy does a half way good job of explaining it