I believe that is B. or the water injection duty cycle you see there. Again just gives you an idea of the shape not the exact flow rate.
% of potential is based on your fuel injector's flow rating at the pump pressure being regulated.
For your goals depending on the load point you would find that from 12% to 20% water to fuel will likely be the result.
If for instance you have 400cc injectors your potential on the fuel injectors is 1,600cc. To make sure you can reach 20% if you needed to you would select a jet combination that have a potential of 320cc or 20% of the fuel potential.
This can be achieved with an Aquamist pump using a 100cc accumulator (even more easily using the STi water tank pump as a primer) and a 1.0mm jet. You could bench test the system to play with the water pressure switch to get that flow by engaging the hsv fully for one minute with the jet in a measuring container.
Now if a particular point is at 70% IDC for the fuel injectors and you put the water injection cycle at 70% also you will be at 20% water to fuel. 52.5% water injection cycle will put you around 15% water to fuel and 35% WIC would be at around 10% water to fuel. The exact percentage on a point by point basis is going to be trial and error. This is because there are very few identical setups to copy across several of the same car and almost none at this point for the STi as to my knowledge in the US none are on stand alone yet.
Starting from the optimal nonWI tune I would advise Phil to use water injection rates at 50% of the initial fuel injection cycle map - this would give around 10% water to fuel across the water injection map. Without fuel and timing adjustments the car will have lost torque at this point. Reduce fuel and increase timing to the new knock threshhold and see where that ends up. As fuel is being reduced the water to fuel ratio will be increasing as well since they are still at 50% of the initial fuel values.
In either case try not to get below 25% water injection cycles - if any points need this low an amount you probably need to use a smaller jet instead and increase the cycles.
Phil has the experience to feel out where adjustments are needed between the three variables from this initial point.
Treat it kind of like race fuel except that you can actually adjust the octane of the fuel itself - the water injection rate.
Invite him over to read this thread as well.
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