Here is a good link I came across it has all the fuel saving devices old and new. You would be amazed how people have brought back many of these old devices as new inventions. They didn't work back then and they don't work now. Even some very crude and backwards and poor attempts at water injection are in here.

Some of the devices will look very familiar to you even though some are 20 and 30 years old people just keep bringing them back to make a few bucks. Some do have minor and I mean minor gains but nothing you would spend money on.

Some of these will look very familar

These were all tested by the EPA in the US.

http://www.epa.gov/otaq/consumer/reports.htm