hornetball

iTrader: (4)

5 seconds is excessive, but a couple of seconds worth is normal. Doesn't hurt anything. Volume isn't really there because the pump is off and pressure is falling quickly. Similar to taking a couple of shakes after you've done your business.

Mr.Pibb

It should stop spraying instantly when the pump shuts off.
Why does yours keep spraying?

Is it because no solenoid and checkvalve?

hornetball

iTrader: (4)

It can't stop spraying instantly -- physics. There is a pressurized volume of fluid in the hose between the check valve/solenoid and the nozzle (I'm using a check valve). Until the pressure equalizes, a bit of fluid will dribble out. That usually takes a couple of seconds (if you are watching a pressure gauge or have a light hooked up to a monitoring pressure switch). Like I said, not a big deal. The pump is off and there isn't any real volume being injected -- pressure equalization only.

Joe Perez

iTrader: (8)

The host which is between the pump and the nozzle is not perfectly rigid. It has the capability to expand slightly when pressurized, so it acts a bit like a balloon.

When the pump is running, it "inflates" the line with water, so the line acts as a pressure reservoir. When the pump shuts off, the line contracts to squeeze out the excess water and return to ambient pressure. It's that process which causes water to drizzle out for a few seconds after shutoff.

If you were to replace the line between the pump and the nozzle with one which is perfectly rigid such that it cannot expand when under pressure, then the spray of water would cease immediately upon shutoff of the pump. The flow of water would also be extremely irregular, pulsating with the action of the pump rather than delivering a continuous stream.

Enginerd

iTrader: (1)

I'm going to try out water/meth soon on my MP62. I'd like to add to this thread on sensor/nozzle locations. For the MP62, it's just the single crossover tube behind the radiator. My AIT sensor location just before the throttle body heat soaks a lot in stop and go (behind radiator, above radiator hose). I worked out the ait/coolant temp compensation in megasquirt so its mainly a nuisance.

When adding water/meth to his setup, I take the better setup would be to relocate the AIT sensor upstream of the nozzle(s). So AIT near the middle of crossover tube or MP62 discharge elbow and the WI nozzle at the throttle body inlet?

misfit77

I have a check valve...that's why the it sprays for a few seconds after shut off.

No check valve would allow the pressure relieve itself in the other direction.

My VW ran that way for over 3 years...nothing to worry about.

My miata gets hotter than a modern VW. I have popped a water line due to pressure and heat........what are you guys using for 1/4 water line?

hornetball

iTrader: (4)

I've usually seen it recommended to put the AIT post-nozzle for the same reason you would want it post-intercooler. You would like the ECU to get a good reading of temperature and pressure of the air that the engine is pulling through its intake valves.

Theory aside, my observation is that the intake cooling effect of injection isn't nearly as much as you might expect. The more alcohol you run, the more cooling you'll see. This is related to how quickly the injected material can change phase -- which in turn is related to how much of the injected material the pressurized air in your intake can actually absorb. For pure water, you'll find that little of it evaporates prior to the combustion event. It makes sense if you think about it -- we're always draining water from our air compressors. If you want to be scientific, look up "psychrometric chart."

While alcohol flashes off more quickly and gives some intake cooling, the overall ability of alcohol to absorb heat in a phase change is about half that of water's -- so you end up with a lot less cooling in the cylinder.

Bottom line, if I were to do it over, I'd locate my nozzle just a little before the throttle and not worry about it's effect on cooling the intake charge. I'd put my AIT just a bit upstream from the nozzle so it doesn't get too wet. And then I'd get on with tuning.

If you really want to knock temperature out of your intake charge (which does great things for HP) you need an intercooler.

Enginerd

iTrader: (1)

Ok, I got my W/I installed and now tested today during autocross. I started with the nozzle located upstream of the MP62 and throttle body. It cooled moderately well. The boost charge heated up and the cooling affect was too far delayed to be effective on and off the throttle. AFR's after my 6th run of the day were up to 175F, but tended to stay at 140-150F during the runs. The charger, piping and intake manifold remained hot to the touch.

Then I switched the nozzle location to the dummy throttle body and removed the AIT timing retard that I had as a safety net for the morning runs. The cooling effect and power was immediately notable. The intake manifold was cool to the touch after each 75 second run. The AIT sensor is mounted at the inlet elbow to the intake manifold...and I could definitely see how much heatsoak had previously been coming from the intake manifold itself and not necessarily the radiator blowing on the crossover tube.

Where to go from here?
I'm going to keep the 3gph at the dummy throttle body and add a second smaller or equal nozzle either pre-supercharger or just after the supercharger.


From what I observed today, injection just before the intake manifold was most effective.