[robbilau]

I am interested in replacing my FMIC with water injection and I wanted to open discussion on how best to do it. I have a turbo Miata with MoTeC M4 Pro ECU and Aquamist 2c.

I have some flexibility in driving the injection as the M4 allows me to choose the axes of a custom table. Currently I use MAP/RPM but I have the following choices:

X Axis (Horizontal):
1 ? RPM
2 ? ET (Engine Temp)
3 ? AT (Air Temp)
4 ? Aux V (Auxiliary Volts)
5 ? Aux T (Auxiliary Temp)
6 ? G Spd (Ground Speed)

Y Axis (Vertical):
1 ? TP (Throttle Position)
2 ? Eff (Efficiency Point)
3 ? Load (Load Point)
4 ? MAP (Manifold Pressure)
5 ? Aux V (Auxiliary Volts)
6 ? Aux T (Auxiliary Temp)
7 ? G Spd (Ground Speed)
8 ? Duty (Injector Duty)


IMO the best option would be to use a second temp sensor (Aux T) and use AuxT and Duty as the axes. Duty will likely be the best indicator of actual air flow through the motor and AuxT will advise how much intercooling is necessary. However it might be possible to use a dedicated PID controller of some sort for this, similar to a boost controller.

Assuming I use the MoTeC map I'm thinking AuxT is at the compressor outlet with a jet immediately after so that the system is reacting to heat before that heat gets to the jet so it has no lag, preventing a burst of hot air from hitting the manifold. This assumes a constant rate of cooling and can't compensate for changes in that rate due to environmental humidity or water temperature. Any idea regarding the degree to which these environmental differences will play a part? I also have one more output so I can add a second jet somewhere else. Will I get better atomization with multiple jets or will I simply be complicating the system? If I do use an additional should they work in sync or be staged with the onset of heat/boost? I could even inject pre-turbo with a second jet (understanding the issues with compressor wheel wear).

Last is the actual piping. I have access to a machine shop so I am not bound to a simple cossover tube from turbo to manifold. I can increase the diameter for example to allow more volume, recess the jets, change the shape of the tube. This is assuming I use metal of some sort - perhaps another material will be better or simple insulation (Thermo-Tec wrap etc.) would suffice to reduce heat soak from the engine bay.

I think that's enough to start the ball rolling. All comments and ideas are very welcome!