The energy properties of gasoline and hydrogen?

im looking to convert my truck to hydrogen hybrid, ive seen many people do this to increase there fuel milage substantially but how much hydrogen per minute would it take to be comparable to gasoline burned per minute at an idle. finding a middle point between small 2.2 liter engines up to 7 liters lets use a 4 liter engine as an example. please help, im not dumb but im no charlie epps either lol.