As a general rule, a naturally aspirated diesel can handle some backpressure in the exhaust. It creates inefficiency. A diesel engine does not "need" exhaust resistance but engineering facts and old timers' lore often do not play nice together. Old time mechanics will tell you that a reasonable resistance in the exhaust flow avoids excessive EGT and burning up valves. I think that there is an enginnering reason that has to do with the hot exhaust gases being pushed into the exhaust, cooling and contracting and creating a vacuum and "shock wave" with every exhaust pulse that, over time, affects the exhaust valves. This seems to be more pronounced when the exhaust is not well matched to the engine. Maybe that is why people think that diesels need "back pressure"?
I suspect that - maybe - that thinking caused the LD multis to get the small diameter exhaust stack?
Adding a turbocharger also adds a bit of backpressure. If you further add a muffler or add an exhaust that runs several feet to the rear you will further increase the "back pressure"/exhaust resistance. Increasing it above the maximum that the engine is designed to handle can cause problems.
Well. Not sure how much extending the exhaust pipe on the mighty LDT really matters in that department. Others will chime in.
