Waste of time and money! Better off just servicing the vehicle @ recomended intervals! Never save enough $ to pay for it. I've installed plenty for customers and if THEY purchased it then, OH YEAH IT IS GREAT! However in reality, it doesent help! They look 'pretty' though, some think.
If you have a one gallon jug and try to pour two gallons in it, it dont work! Now if you increase the size of the jug you start out with, then it can take on more!
In other words you would have to increase the entire intake capacity of the engine to do any good. Then you need more fuel! Think about it. Google "air fuel ratio"! Your engine is already designed/programed to obtain the optimum A. F. ratio 'IF' maintained properly!