yes, mid 2000's... emission stage one..
particulate filters and urea injection will only increase the total cost per mile: An efficient combustion is one with an excess of oxygen, resulting in total, full combustion at hot temperatures. Hot combustion will result in NoX.
To decrease the NoX manufacturers have to lower the combustion temperature by lowering the oxygen content of the air (but still putting in enough air to combust) so they recirculate exhaust gas into the intake, to take in the same amount of oxygen but mixed in a greater mass of air.
All in all, lowering NoX emission means moving away from the engines most efficient combustion, thus increasing fuel consumption. SCR also has to be payd for, and the total fluid consumption (diesel plus AdBlue) will increase over that mid 2000's diesel.
And that mid 2000's diesel you said, had 130hp which is something different than 300hp you guys are wishing....
I have been to sales meetings of engine manufacturers, and they wont deny that we are already over the peak of fuel efficiency in internal combustion engines, due to emissions. It wont get any better than stage 1 high pressure direct injection engines.
I guess the reason that Dodge doesnt put that QSB4.5 in a 1500 and 2500 Ram yet, is because the 4 cylinder doesnt sound very classy in a big pickup truck.
We do get them in Europe, badged Paccar, in the DAF 45 line of small/medium duty trucks.
Toyota had the 4.2 liter inline six. If they upgrade that to the engineering standard of the D4D engines, it will be a winner in a Tacoma...