Ther current water injection system is quite basic compared to the advancement of fuel delivery system to date. Direct in-cyclinder injection will soon be taking over all the current fuel manifold injection system. Only a handfull of high-dollar cars are using them at the moment.
This trend also means the WIA injection system are falling further behind. Most budget system on the market is still uses a pump speed system that will not be able to cope with fast transient and wide dynamic range (load). For those system, it relies on the tuner to make up the AFR gaps and produces a less than perfect tune. As far an most people are concerned, they are only interested in the peak power figures.
At 7000 RPM, I believe the injector has to respond to 120Hz, if they are batched fired. But if you can put up with the expenses of having four inline valves and fire them sequentially, they only need to respond to 30Hz intervals between each event. Of course a manifold pressure compensated water/alsohol line will improve the set up further.
We can design and supply a fast acting valve that will match the fuel injector's flow. opening and closing time, but I don't think we have a large enough market place to justify developing such a system. We have already attracted quite a few negative comments on our current IDC system, based on jusy one fast acting valve. I guess you can see where the trend is leading ... not the direction you are looking.