Quote Originally Posted by DFBrews View Post
C stone

what the def does is reduce the nox emissions in the exhaust pipe instead of in the engine
to reduce nox you need to have cooler cylinder temps which is done by recirculating some exhaust back into the intake.
now with a system to clean up the nox on the back end higher cylinder temps means higher efficiency and much less egr recirc.

On the 15 liter Cummins 2008-2010 engines recirced up to 25% now with def that number is in the low teens
Does that make the engine more efficient? More MPG or more HP per gallon of fuel burned?

It seems that the more NOX reduction the more CO2 produced and vice versa. Pick your poison but I would think that burning less fuel is the best route.