Please excuse my utter ignorance of most things engine tuning.
I'm going with the the ECU that Ed mentioned, the Element-Hydra, with maps from Phil Grabow--former TurboXS employee. I just bought a Aquamist 2d from Ed. I have the USDM WRX STi 2.5L EJ257, and I too would like to use the ECU to drive the water injection system.
The Element has fuel injection controls as well as a few "extra" controllers for things like water injection.
I'd like to set up a 3D map for water injection but I am at a loss as to what parameters will be best for the ECU to track and alter water injection to suit the engines needs. RPM and boost are givens for water injection, but I'd like to add in something like EGT temp or air temp at the throttle body, scaling water injection when temps rise.
Let's say we use: Load x Boost x RPM x Temp at Throttle Body (TTB).
The water injection map will mirror (scaled down) the fuel injection duty precisely according to the tune without WI plus additional water as boost increase. So load and boost go up so too will the percentage of water (I think). Let's say at a load value of 2, boost value of 3 psi we will inject 5% water (as a percentage of fuel) across the RPM range (that is the 5% value holds, but more water is injected as the RPM increases with the fuel injector duty). At full boost, say 17 psi, and a load value of 5, we will inject 15% water (the load and boost have consorted to raise the percentage from 5% to 15%). Now I'd like to scale water injection such that an addition 1.5% of water is injected for each 10 degrees C above 40 C TTB. So, if the outside air is 40 C (100 F) instead of our usual 20 C (here in Seattle), the controller would be injecting an additional 3% water changing the injection range from 5-15%, to 8-18% of total fuel.
I have three basic questions:
1) Am I crazy, does it matter to scale with outside air temp, boost, and load?
2) Where do even begin with the 3D map values (I can't find any 3D water maps)? How does one develop such a map?
3) Let's say I manage to get a 3D map from someone (maybe from Richard L) do I need to worry that this 3D map is good enough for my engine, with my mods, etc?
I basically think that the "customization" to my mods will come from paralleling the fuel map (and anti paralleling the fuel dumping). So I think question 3 is answered to some degree.
EGT seems to be a means of developing a water injection map, but the number of test points to create such a map is just mind boggling. I can't imagine injecting water at each load, boost, RPM value to the point where EGT is lowered, and then backing off on fuel to reach stoichiometric, then adding water back to lower detonation if needed.
From what I have read a fine tuned map like I describe using EGT is not necessary; there is a fairly wide range of water percentage for each point that will "work". None the less I think a finely tuned map would not be unwelcome to the community. (Cylinder pressure based map has been discussed, but it's a pipe dream right now).
The first two questions are totally up for grabs. I'd be interested what percentages of water injection the TEC3 users are using and why/how they decided to go with those values.
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