"NetSock" wrote in message ...
There are specific cautions on doing this test at speeds above idle in the
Detroit shop manual that I have, and the reason is the blower oil seals.
The engine will draw vacuum against the shaft seals in the blower and they
are not designed to seal against that.

2-stroke diesels do not produce a vacuum.

There is a vacuum produced "upstream" of the blower - the fact that
the blower is sucking air into the engine tells you there is a vacuum
somewhere. It just isn't produced by descending pistons.