anox195
If you haven't been there yet go to
http://www.smacksboosters.110mb.com/
This guy has got more on the internet than anyone. He builds, test, documents, and uses them on his own vehicles. Click on every link you will learn something you didn't know before.
When I checked last I think he was getting 3-4 mpg better with the booster.
Check his YouTube stuff too.
Check the booster rally results. Larry Boyce has a 61 plate booster he runs.