Good question, I think the VWs are a high
speed engine, can probably hit 4000 RPM
but I don't know what the design spec for
a Yanmar or a ThermoKing engine, I think
about 3000 or more tho depending on the
stroke of the crankshaft.
The big diesels like the one I drove, 12L
Cat C-12 are 2000 max, and work at 1200
to 1800 RPM but these engines produce
400-475 HP and like 1200 Ft Lbs Torque

And that my friend will move you and 80,000
down the road while getting 7 MPG.
Wild