Just curious if anyone knows. The walnut blasting/cleaning of the head and intake valves. Is this done with the head ON the engine, or is it removed? I do find it interesting that in most warrenty cases for cabon build, they replace the head rather than clean it (I expect it is cleaned at some point and made available as a refurb replacement).
I'll presume there is no way to meet emission standards, even with more DEF usage, without resorting to EGR (I would go for that!). Am I correct that the primary need for EGR is to reduce NOx?