I see 200-300 degrees of cooling, and I still have the grid heaters. I'm spraying in the part where the stock intake point's up.
I've never heard a conclusive, satisfactory explanation of how it works. According to intake temperature readings, we know that water drops intake temperatures below water's boiling point, so that implies that at least a large part of water's cooling comes from convection- direct heat exchange between the surface of the water and the air vapor.
Obviously that would mean that we want as fine atomization as possible; to increase surface area.
I would naturally think that would also mean that we want to give the water as much time as possible to absorb heat; that would mean to mount it as close to the turbo as possible. BUT, it seems that nobody does that...
When a finny intercooler is added to the equation, I would believe that you would want to spray after the intercooler, because that funny restriction would cause the water to drop out. (That could be confirmed and further tested with a ballcock tapped into the bottom of somebody's intake piping...) But, even the non-intercooled guys like to spray right into the head. Is that only done for the sake of tuning flow rate for each cylinder? Possible. I have seen set-ups spray into the head and the cross over. (I wasn't aware that anybody had nozzles of precise enough diameters to tune flow-rate per cylinder...)
Why would we want to spray water directly into the cylinders, and not give it as much time as possible for heat absorption? I don't know. Either to tune for each cylinder individually or to keep it from dropping out are the only things I can think of.
Which leads me to the second thought; why not force it to drop out somehow? Put one of those automatic water draining ball cocks that big rigs have in their air tanks on the bottom of some kind of centrifuge arrestor piping? Hmmm... If we dropped most of the water out of the charge before it entered the combustion chamber, we would never have to worry about hydrolocking (and could recycle the water). Not to mention we could isolate the results of the water's convection, from whatever results from having the water present in the combustion process.
1990 D-250 Regular Cab: Tweaked injection pump, built transmission, a cataclysmic charlie foxtrot of electronics, the most intense street-ran water injection system in the country, and some more unique stuff.