It appears that ~4-5 degrees of advance increase NOx emissions by a factor of ~1.5-2.2, but like ya said, they also decrease particulate emissions by a factor of ~.6-.8. What's really interesting is that the most significant factor influencing peak efficiency wrt timing is the injection duration. Naturally advanced timing allows for a longer injection period assuming we have the same end. It also seems that breaking pressure alone doesn't significantly influence efficiency, we need to look at running more fuel w/ less air in order for higher breaking pressures to result in better efficiency.