You have to adjust them by the little screw at the top. Anticlockwise for fuel saving and clockwise for power,
Wind it back to far and it runs lean if thats the right word.
I just leave mine in the middle.
The most noticable car of mine it has worked on is a Skoda 1.9 SD so no turbo.
I use it as a shopping trolly.
It is only something silly like 67 bhp and 90mph top end.
By fitting the tuning box it made it go like a turbo.
25 mph on the top end but the mid range is were you notice it.
The guy I got it of borrowed it a few days back and was amazed at the difference.
I still have one for a pathfinder laying about.
They are a lot cheaper than going for a remap and the beauty is you can take them off in 5 mins.