I would suggest that you're looking at a manifestation of adiabatic
cooling.  As air rises in the atmosphere, it cools at the standard adiabatic
rate of 3 deg F or 2 deg C per 1000'.  That's equivalent to 3 deg F per inch
of manifold vacuum.  Idle at 2000 rpm can generate around 15" of manifold
vacuum and that converts to 45 deg F temperature drop.  That is waaaaaaay
more than the dew point spread in most places.  A lot of the heat (and
therefore temp drop) gets absorbed by the warm environment, but not all.  It
is the same phenomenon that causes carb ice.
Just a theory .... Jim S.

Rino wrote:

> An interresting observation about my turbo 13b installation.
>
> While running the engine to check out the systems I noticed that my
> intake runners become real cold, actually they sweat from the
> condensation on the outside.
> I have an intercooler but there was no airflow through it since the prop
> is not installed yet.
> I reason that the air is compressed by the turbo -- heated up then had
> time to cool a bit before getting into the intake manifold where it
> would expand and cool rapidly and would cool the intake runners.
>
> The intake runners were very cold to the touch.
> The engine was running idle to about 2000 rpm at the time.
>
> Rino
>
> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html

--
Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T