[sambeeb]

I guess I should get it out there that the primary reason that I installed water injection in the first place was to mange high inlet temps. That is why I sited the nozzle just after the intercooler so as to give it the maximum time to evaporate and do its thing and hopefully all be in suspension by the time it got into the plenum so that cylinder distribution would be good. The flash tunes I've run are always fuelled up and I didn't think they were ever running lean enough to be able to run a meth mix which introduces a second fuel.
Its very possible that I may have buggered up my calculations but at 230hp/320nm, I worked out that the 0.4"A" at 80psi was flowing the right amount of water at peak torque. I was always concerned that as boost trailed off towards redline and injector duty cycle dropped off that I would then be running too much water up high, but on the last tune I never lost power doing this. But like I said maybe I had under rated it slightly.
After a bit more investigation I'm also seeing a slight 'flat spot' around 5000rpm where the rate of air flow slows a little when I'm not running water. Then when I run water even with the timing advanced, this flat spot turns into an actual dip where the air I'm flowing g/s through the MAF will actually decline for a few hundred rpm, even though no timing has been pulled there. This leads me to think that at the fuelling the tune is running, that like you say, the water is slowing the flame front and decreasing the cylinder pressures too much.
Your last comment regarding the boost and cylinder pressures a 1.8T can take without needing water leads me to think that water is just not going to work on this tune unless the boost is increased. Fuelling is fixed, and it seems timing limited. 1.4bar sounds like a lot but this is being pushed by a very small borg warner KO3s turbo that isn't moving a lot of air in real terms so perhaps that's where i'll look next. A tad more preload on the wastegate should achieve that - I only have 2mm at the moment.
The only other alternative I might have is to switch the water on at say 1.2 bar. That way the water will kick in approaching peak torque and then switch out soon after because with my turbo the boost trails off quite quickly towards redline being so small. Then I might not kill off the top end with too much water.