[hawk2100n]

Originally Posted by ConnClark

Fortunately on a diesel the laws of Thermodynamics don't limit us too much. Adding 10 psi of boost with a roots blower can still improve fuel economy.
http://aerade.cranfield.ac.uk/ara/1936/naca-tn-569.pdf

Edit more proof (page 18 in the pdf)
http://naca.central.cranfield.ac.uk/...report-577.pdf

The OM 617 in your 300SD is one of the last common engines with precombustion chambers. I had a 300TD. But the best way to drive these cars for max fuel economy is below the onset of boost when possible, which is hard. Same goes for all diesel engines. Turbos are for power. I usually got around 27 mpg in my wagon. It's still in the family. My dad is hanging on to it but he and I bought it together when I was in high school. 230,000 miles on it now.