[rotrex]

Boosting a 1800cc Datsun engine to 500HP I would not call conservative.
When I was trying pre turbo on my Rotrex C30-94 I found that 0.5mm jet gave IAT fluctuations. The sensor was mounted after the charge cooler. this indicates bigger droplets accumulating on the IAT sensor. A 0.3mm jet did not yield such fluctuations.
To me it sounds odd that you run a modern port fuel injection system and then combine it with single carburetor style water injection, but without the manifolds designed for wet flow.
Can be done, but needs a different spray spproach.

Again, skip that post IC jet. I won't do much.exept getting you an unequal water and methanol distribution = unevenly distributed knock and AFR rates across the cylinders.

At your boost level, you would also be well suited for a air assited system such as what riceracing is offering. It would simplify your setup as it gets away with mutiple jets, pumps etc. its very fine mist makes it resonably uniform even trough dry flow intake systems.
The trick is that it starts with a very fine mist, much finer that pressure driven nozzles, and sprays it into the turbocharger. Here a big fraction of the methanol and some of the water will evaporate making the mist even finer. This fine mist, probably better called fog :-), stays reasonably well suspended in the air stream and makes it into the cylinder.

Now you run significantly more boost (3+bar?) and with its much higher exit temperatures. I may swallow a bigger jet with flow rates of 150 or even 250cc/min.

Still at first I would only run DP to see where it gets you.
Rob's Evo in the link i posted did not gain any power anymore with more ignition advance. At his current boost level of 1.85bar tapering doen to 1.55 bar (realtive) he is not knock limited anymore and can run an optimal ignition timing. He achieved this with 4x 0.5mm jets and some 5 bar differential spray pressure, so just some 600ml/min total. He said he will increase boost next.

The total flow of mix only tells you half the story. The other half is how much of this flow rate makes it into the cylinder as actual mist and how well it is distributed.