I've owned diesels with both the R-4 and Nippondenso compressors. The cars with Nippondenso compressors don't seem to be as affected by compressor drag, but it's an apples & oranges comparison. We're talking about different chassis with different engines. It probably has more to do with the engine - OM603 vs OM617.

BTW, the Nippondenso isn't really a rotary compressor. There are five little cylinders in there with pistons boinging back and forth. The cylinders run parallel to the length of the compressor case, and are arranged around the circumference. Likewise it's my understanding the R-4 is a four cylinder compressor, with the cylinders arranged in a radial pattern, like a radial aircraft engine.

Isn't a true rotary compressor more along the lines of a turbine?

- JimY