well, black smoke is a telltale of a LOT of unburned fuel....(in gas engines anyways, i assume diesel as well? my diesel experience is failing me at the moment)

to some degree it's necessary to keep combustion chamber temps under control when under heavy load, but to the extent that they're going, they're sending a BUNCH of raw fuel out of the exhaust.... idiots. i've seen enough diesels with "smoker" tunes myself. i'm kind of amazed it took this long for the hammer to fall.