Firstly, I dont claim to know very much about water/meth injection. But I have read that the water can have a negative effect in relation to making the motor deteriate quicker. That being the moist conditions can cause rusting to components. I know that you are going to say that the 1UZ is alloy, but not all of it.
Does the roots type chargers build up boost as the revs increase like a turbo, or is near max boost from opening of the throttle. If its the earlier type, why couldn't you have a supercharger that makes 12 psi (or whatever you want) and have a hobs pressure switch kick in at around 7 psi and above to supply the water/methanol injection.
I'm looking at intercooling my M90 1UZ when i fianlly have all the parts and water/methanol would be a lot cheaper and easier. I will have to do some more research myself. Had a quote for the Laminova type water to air intercooler setups for inside my manifold that I am going to make and was shocked at the $2000+ price :censored:
Kev