I once built a B series Cummins for a Bristol Bay fishing boat that I dyno'd around 400 HP, and with the lights out in the dyno room the turbo housing was "transparent" enough when glowing red, that you could make out the exhaust turbine spinning inside when you back off the throttle. It was the coolest thing Even that hot rod engine would only black smoke when you would hit it with load, and only for a split second. It was part of our tuning process to watch for smoke. Some engines would smoke more than others, when picking up a heavy load, but it certainly was not ever desirable. Engine life is really calculated by gallons of fuel burned; not mileage, or hours. Those high horsepower diesels I have built, or sold to customers easily had half the lifespan of a lower horsepower engine from the factory. Coal rolling pick-up truck engines are no different. You should see what the top of a piston looks like on an over-fueled diesel engine. It is not pretty, but hey, he got to smoke out everybody at the intersection.