The correct answer is NO! But that does not mean it cannot be done!
There are many factors which go towards determining the level of economy in any vehicle. Some are–:
The driver The year model Gasoline or diesel before on-board computers or after how well the engine runs (truly!)
Having said that, you would need to give Make, Model, Year, Fuel-type and engine capacity (litters or cu.in). Then it would be possible to assist you in determining which type of HHO generator you should install, and typically, why sort of savings you are likely to get! I always say,"You should be able to expect 25%, IF your car engine is in A1 condition. You might well get more. I am getting 49-50% with MY 2002 VW Bora 2L 4-cyl gasoline engine using a 7-plate slimLine generator producing ¼LPM or 0.25 LPM which is enough for my car!"
Good luck.
Response From by: Hydrogen-Generators-USA.com
It is not typical, we do have some customers that have doubled their MPG.
You don't say what size engine, but usually a passenger vehicle will see 25%.