[b_boy]

I'm starting this thread in the hopes of developing a Tuning Guide that could be a Sticky in this Forum.

Folklore has it that for now EGT is the best method of monitering the tuning with water injection. For us novices, some understanding of a tuning "algorithm" would be of benefit. I'm going to start with a straw-man approach, posing a method to use as framework for further development.

1) Tune the car for power without WI, no knock.
2) WI turns on at 3-5 psi boost.
3) Add water injection in the 10-25% range (ramping with boost is good).
4) Remove fuel until (an unobserved, but inferred) 12.5 AFR is reached, watching EGT.
5) EGTs should not rise above pre-WI temperature.
6) Advance ignition until knock is detected, watching EGT again.
7) If 12.5 AFR cannot be reached without knock or high EGT, stop reducing fuel.
8) Advance ignition or add more fuel to reach optimal power even at sub 12.5 AFR.

The parenthetical comment 'unobserved, but inferred' comes from the idea that with water injection on the oxygen sensor cannot be trusted. One may however subtract fuel until the ratio has reach 12.5 by simple subtraction of a percentage (e.g AFR 10:1 --> 12.5:1, subtract 25% of fuel at 10:1).

Now one thing I've notice in the various "calculators" I've browsed is that more power can be had with lower AFR than 12.5. While this is the fuel ratio of optimal power per gram of fuel, it may not in practice be the AFR of best power. So, I question the assertion that 12.5 AFR should necessarily be the starting goal for best power.

Also ignition advance is a moving target. The peak torque achieved during a combustion cycle varies across the RPM and load range (by only a few degrees probably). At some point more advance will become detrimental to power and especially at high RPM when valve timing will necessitate decreased advance.

None the less, in my steps 1-8 above, I have taken as a given that 12.5 AFR is the number to shoot for, and that ignition advance is used to achieve optimal torque once the "optimal" AFR has been reached.