More Water, More Air Flow ??

[PuntoRex]

I got an insteresting observation.

I have a pre-compressor injection setting on my car, switched in when high flow. The water route control solenoid is driven by a voltage comparator, which monitors the MAF signal.

The switched in point is set at approx 4.2V, which is when 5000rpm WOT. (max signal voltage is 4.65V when WOT to redline)

Yesterday, the weather got warmer, so I dialed up the W/F ratio by a pulse width adjuster before my FiA2. The estimated ratio was raised from 22% to 25%. (with injection D.C increasing by 10% around this region)

The additional water alone made the switched-in point earlier to somewhere between 4200~4500rpm.

The switch threshold should be a consistent 4.2V, which reflects certain level of mass air flow. Now it happens at somewhat lower rpm, so it means the engine flows as much as 5000rpm at the old days with only 4x00rpm now?

I didn't notice the boost rise, it still holds slightly higher than 20psi as usual.

Could this be possible? Or have I misunderstood anything?

[hotrod]

It seems reasonable to me. By precooling the mixture before it hits the compressor and increasing the compressor effeciency ( with respect to mass flow) by having a cooler moist air charge to work with, it should flow more air at a given exhaust flow.

Although I did not get instrumented results like yours, by seat of the pants analysis matches up with what you're seeing.

Larry

[PuntoRex]

Well, maybe I didn't make myself clear enough.

That is the point when the pre-compressor injection kicks in. So, before that, only pre-throttle injection is working. (I have nozzles at both ends)

In such case, can we see it this way:

The boost controller maintains a mostly constant boost "pressure", regardless of the "temperature". So, when we cool the charge at the same pressure level make it flow more.

And the cooling is bought by more water.

It just surprised me by such a margin.