I found this web site while searching on Google. Because sometimes is difficult to find things on the Internet, here is the link:
http://www.smartnouveau.com/Sentra-Pathfinder.pdf
(wait a little until it downloads in Adobe format)
It shows a manual from Nissan, but apperently intended for
their Service Managers, Advisors, and other Nissan employees.
But, if it is available through the Internet is because someone at Nissan decided it is useful for the General Public too, beacuse it describes the enhancements of the new Nissan Sentra 2000 + 1.8 lts engine over the GA16DE engine. It also includes the same information about the Pathfinder and the SRD20E engine.
This might help anyone to understand how things are now, and why because it includes brief explanations and diagrams.