A lot of googling..
If I read this right
http://www.nj.gov/dep/aqm/eimp297a.htm
LVW HC CO NOX
3375 162 0.91 1227
3750 148 0.83 1110
The difference is vehicle weight, not necessarily engine type. So it appears the 2 cars have different listed LVW thus different standards. It seems this came in as part of the roller tests. It did not used to be like that.
There is no ideal timing, every engine setup is different. You have a cat in the car?