SO difference
THIS IS THE STATEMENT I RECEIVED FROM POWERMASTERS ON THE SUBJECT.
Summary: ram isb CARB ratings by year
Solution:
Thanks for the email. The primary difference is more retarded timing, which reduces engine efficiency but does lower peak temperature for lower NOx. This also causes increased soot loading of the oil, as the fuel gets quenched by cylinder walls and produces more soot in the oil.
A lot of the exhaust energy is absorbed by the turbo; the increased back-pressure from the converter is not likely much of a penalty.