I disagree on the potency of the gas... Hydrogen is a big bang...

From the info stan released about the buggy, it consumed 44,4ml of water per minute at 3000rpm at 100km/h or so...

At this 3000 rpm You have combustion in a pair of chambers in during the first rotation than another pair at the second turn... so you get 1500 combustion cycles in each chamber or 6000 combustions per minute...

If now we assume that round value that water in gaseous form become 1800x bigger, we take the 0,0444L per minute multiply by 1800 we get around 80Liters per minute of oxygen hydrogen mix, now divide this number by 6000 cycles per minute... we get only 13,3ml of gas per injection... which represents 7,4microliter of water per injection.

If you get a 1600cc engine it get 4x 400cc chambers

do you see is not really much gas per injection?