Over scavenge TD exhaust?

[TraceF]

My understanding is that a turbo diesel does not require exhaust back pressure like a gas motor. Too little back pressure will actually harm performance on the gasser. A turbo diesel will in theory run with no exhaust system at all if you could stand the noise and heat.

One of the aftermarket diesel parts retailers told me the opposite yesterday. I think he was trying to change my mind about the exhaust system I want but also think it is worthwhile to ask the question to all of you...

Can a diesel engine be over scavenged? Does it require back pressure? If someone built a 6" exhaust system would it work better or worse that the common aftermarket 4" systems?

Thanks for input.

[Kennedy]

I believe that your first paragraph is correct to a point. While a turbo engine does not require back pressure to operate, you still need to size the pipe properly. If you cannot fill the pipe properly, and allow gasses to stand still or slow down, the rush of new exhaust can meet with resistance. I also feel that fake duals can actually hinder performance. Basically, I believe that the exhaust gases should remain in a single column and in a pipe suffficiently sized to carry them with minimal back pressure while MAINTAINING velocity. I think splitting into a dual tail tends to confuse and misdirect the gasses quite possibly causing reversion from one pipe to another. With the split "scroll" in the turbo, the Dmax seems to have a less than smooth exhaust flow so there will likely be a bit more "pulsing" that a conventional turbo.

Note: I am not an expert on fluid dynamics, I just play one in my dreams some times :D