Water injection is only needed where detonation is a problem. Usually this phenomenon occurs at turbo boost levels exceeding 10 psi. The injection should always take place in the manifold and this requires a pump that will produces significant pressures above the boost which you intend to run. There was an article for a DIY water injection system on one of the links on the turbo Regal. Buick Grand National website. An adjustable pressure switch can be used to turn on the system,
a sprayer pump used to generate pressure, a nitrous nozzle for the fogging, and an overflow bottle to hold the water mix.
While H2O injection ( or more ideally a water alcohol mix) can be used to great advantage to control detonation with a turbo, you may find that it may slow you down a bit when used when it's not needed.
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87GT 3.4 Turbo Best 0-60 5.2 seconds
http://www.turbochargerpower.com/turbo.htm