I want to share my new result. I did Range Rover with Jaguar AJ-V8 4.4 engine (2006).
Before the groove it wasted about 18 liters / 100 km city and 14 on a highway.
Too hungry car
After as computer showed numbers went down to 14 in the city and 11.5 on a highway.
So the owner is happy. He does feel increase of power slightly a bit