[ever_green]

No I have not started following this chart yet. I still have to do more logging and confirmation of the numbers. I find that stuff like temperature and humidity play big role in this. For example the ECU disables EGR at freezing temperatures. This increases combustion efficiency considerably.

With EGR enabled though lower loads are generally more helpful to help 'evacuate' the dirty gasses in the combustion chamber.

So this chart is for winter use and I am still logging and constantly changing the above chart. The changes are minor though. For example a test run last night indicated that on a fully stock impreza the BSFC sweetspot is "taller". What i mean is that the BSFC sweetspot is anywhere between 85-99% load at ~2000rpm with stock ecu but with a modified ECU above 90% load fuel enrichment causes a dip in mileage (open loop delay is removed). This open loop delay was removed to increase engine reliability and prevent knock. Knock actually further depreciates engine efficiency since factory tune is very aggressive timing wise and whenever knock is detected engine cuts considerable amounts of timing thereby killing volumetric efficiency across the powerband. But because the tune solves the knock and ignition retard problem my overall BSFC is better with a tune at 0.45 vs 0.47, just the sweetspot island seems smaller.

My findings basically indicates that no matter what bells and whistles your engine has, vacuum is #1 enemy to BSFC. Then it's fuel enrichment followed by ignition timing and engine speed. So i just accelerate now with highest possible load without going open loop, which is around 85-90% engine load. I try to keep RPM as low as possible which is usually 2000rpm. Lower RPM not because of just friction but because Open loop is entered more easily at higher engine speeds. I only accelerate at lower loads if i Know I will come to stop soon (redlights, stop signs, traffic). So yes it has improved my mileage by fighting vacuum when appropriate (ie merging or pulse and gliding on a long highway stretch).