To see how backpressure effects a diesel you can dig through this research paper.

http://naca.larc.nasa.gov/reports/1937/naca-tn-619/

To summarize the findings with respect to back pressure for you

A diesel is less sensitive to back pressure than a gas engine.

Turbochargers and diesels are a great match.

Basically when it comes to back pressure on a diesel, a drop in back pressure gets you a little more power. As back pressure increases the power from a diesel engine drops off at an increasing rate. In other words its an exponetial function.

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