Larry,

There is something extremely peculiar about the airflow around your pipes.  The discoloration pattern is very unusual.  Look at other standard pipes and the discoloration pattern usually indicates good streaming of the cooling air joining the exterior cowl air flow parallel to the fuselage.

Do you have another picture with more of the cowling in it?

When one adds a cargo pod to the bottom of a Skymaster, the exhaust pipes must be turned to point straight down to avoid heat and stains on the pod.  If the pod is removed, the Skymaster will continue to fly about 5 mph below book values until the exhausts are returned to their rearward flow position.  Apparently, the downward exhaust column provides significant drag.

Scott Krueger
N92EX