New Ram/Cummins vs GM/Duramax on the IKE

FishOnOne wrote:

As for the high fuel pressure I agree it helps with reducing emissions so HP can be increased, but you said that higher compression ratio increases an engines efficiency which makes perfect sense. I'm wondering if the reduced compression ratio is more about improving emissions while supporting more HP, at the expense of efficiency.

Yes you are correct that they had to decrease compression ratio in order to increase power while meeting emissions, but htis can be negated some with increased fuel pressure. This is why only the high output Cummins with the Aisin has the lower 16.2:1 ratio while the standard output with the 68RFE has actually increased its compression ratio to 19:1 compared to previous years. I bet you would get great fuel mileage if you tuned and deleted the 68RFE version of the 6.7L. And all the power that could be had if you removed all of the stock de-tuning just to meet NOx emissions.