Based on the calculated diagram below, you can gain 2.5 points by injecting 3% of water and retain the same latent heat's cooling effect of gasoline.
3% of 5250cc of fuel = 157.5cc of water.
But there are other factors involved such as the combustion temperature increase rapidly as you are leaning off the AFR toward 14.7:1. (stoichometric of a perfect burn). Depending on the homogeneous of air and fuel distribution and the spark power, misfire will occur much earlier before 14.7:1 AFR, so 12.5 is about the limit of a non-leanburn combustion chamber design.
In practice, 12.5 is the ideal and injecting 3x the theoretical cooling value of 3% or 472.4cc/min), just to be on the safe side.
You can adjust you ignition to suit always go towards MBT. Adding methanol is good way to bump up the octane of your fuel. As suggested on the previous post
Here are more charts below for you to chew on. So always inject 3x or more as methanol concentration increases. (Latent heat of water is twice as methanol)
Further readings
http://www.aquamist.co.uk/vbulletin/...ead.php?t=2187