Shinerbock, I have really learned a lot from your posts. Thanks for hanging in. I have a 2012 6.7 Cummins. I don't like the smoke I see from most deleted trucks. I don't need more hp or torque. I have a limited understanding of the EGR system. My question is, how is returning oxygen depleted hot air back into the combustion chamber a good thing? Is that what happens or am I missing a lot of what is happening in the system? If I block that part of the system, does it have detrimental effects on the rest of it? Thanks, hope you don't mind the brain picking