Here's what the federal government had to say about ZMax.... it ain't pretty.
http://www.ftc.gov/opa/2001/02/zmax1.htm
And about other "additives/devices"
http://www.ftc.gov/bcp/conline/pubs/autos/gasave.htm
http://www.ftc.gov/opa/2001/02/zmax1.htm
And about other "additives/devices"
http://www.ftc.gov/bcp/conline/pubs/autos/gasave.htm