I found some very interesting links. One even states that someone who ran some formal sounding tests got a 20.8% increase in power output.

Here's some links:

link1
link2
link3

Even if not for power increases, I've heard that the water injection process does wonders for carbon removal and engine cooling. Also heard that years ago, GM or Ford or whoever even used to sell WI systems on standard street cars.

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Chris
1985 300SD - 'Grace' (198K mi.)
2018 Honda Civic Sport
2018 Honda CRV LX
2010 Honda Fit Sport (RIP)
2013 Honda Accord Sport (Sold)
1996 Lexus LS400 (Retired)
1995 Ford Contour SE (Retired)
1976 Porsche 914 (Sold)
1972 Datsun 240Z (RIP)