Thoughts on Cummins 5.9 -> 6.7 vs Detroit 12.7 -> 14L (EPA & EGR)

Thanks for reading this post. I was asking on an older thread but want to invigorate the discussion.

It is well known that in 2007.5, Cummins took the 5.9L 24V and added EGR to meet EPA requirements. To compensate for the lower HP, Cummins bumped up the displacement on the ISB to 6.7L. but everyone says that fuel economy took a big hit.

That got me thinking. That's exactly what Detroit did in 2008 to the 12.7 Series 60. Added EGR and bumped up the displacement to 14L. Just like Cummins, fuel economy took a big hit.

So here I am with my 2008 14L EGR engine thinking about reverse engineering the Detroit to enhance the EGR with some blocking plates and reduce the displacement to 12.7 AND get a fuel economy boost. Throw on some performance mods like extrude honed EM, BW 171702 turbo and maybe injectors and the 12.7 L can even put out better HP and torque numbers than my 14L EGR.

Heck, why stop at 12.7 L, maybe going to 11.1 L would be even better?

Corky on this post says that the DD13 and DD15 get the same MPGs, even though the displacements are different.

Cascadias with dd13 and dd15 mpg

Just want everyone's thoughts.

 

OK. This makes sense to me. I was pretty sure that both EGR and displacement contributed to the lower fuel mileage.