Originally Posted by
Painless
Simplest way, get yourself a bottle that you know the capacity of, i.e. a 500ml or 1 liter plastic bottle. Fill a bucket with water and dunk the plastic bottle into it until full. Turn the bottle upside down (opening downwards) and insert the HHO tube into the end of it underwater (start your stopwatch). Once the bottle is emptied by the HHO gas, stop your stopwatch. Now you know how long it takes to create a known quantity of HHO. Some simple math will yield LPM.
Gorgeous MegaCab, by the way!