Interesting results Mychailo. I guess that graph explains a lot of my findings with the Impreza fpr as well. However, based on my dyno runs with the stock fpr last December, the richest the afr ever got was ~13.4:1-13.3:1 at WOT above 5000rpms.
It's interesting that the afr centers around 12.5:1 and then becomes even richer in the upper rpms! Per an article in SubieSport Magazine a few months back (when Huck369 was first featured), an afr of 11.6:1 or richer is needed to safely run an extra 5* of timing advance...
Maybe I know what my next mod will be!
-Chike
P.S. I was doing some calculations the other day and realized just how much more fuel our engines would get in open loop by raising the fuel pressure by ~7psi.
Our injectors flow 275cc/min at a fuel pressure of 36.3psi
If the max fuel pressure is raised to 43.5 psi, then our injectors will effectively be able to flow: 329.5cc/min
Moreover, if people have estimated that 275cc/min can support 250hp on the motor, then 329.5cc/min should be able to support 295hp (assuming a linear relationship).