Lee is right about the 1/2 your engine displacement rule of thumb, but depending on your vehicles emission control devices (or lack of them) some engines respond to higher levels of HHO. My car seems to.
Therefore, I recommend building a system that will produce 1 lpm of HHO for every liter of engine displace (1.6 lpm in your case, but when you install in on your car, reduce the current so it only produces 1/2 lpm HHO for every liter of engine displacement (.8 lpm in your case) Run at this setting for a few tank fulls of gasoline to give the HHO time to clean our your engine and for the MPG to stabilize. Once you have a stabilized MPG baseline, start increasing your HHO production a bit at a time to see where your engine actually performs best.
Steve
1991 Plymouth Acclaim 3L V6.
1 dry cells with nineteen 6"x8" 316L ss plates, driven by constant current PWM set at 35 amps (13.3V at PWM). 28% KOH electrolyte. Total measured output 2.5 lpm. Mileage went from 18 to 26 mpg, all city driving (44% increase). EFIE set at .370 and I still need to play with ignition timing.