RE: Exhaust extension
The outlet of most mufflers can be rotated to direct the exhaust away from the airplane, which is usually enough to keep it relatively clean. However where that is not enough, an extension may be used. The two photos show examples of extensions from my fleet. The first is on a PAW 19 diesel. Diesels are particularly dirty with oil that is dark brown. Before fitting the extension I found myself leaving this airplane at home more often than not because cleaning it was such a pain. With the extension, the bottom of the elevator is the only place to collect much oil.
The second picture shows an extension fitted to an MDS 46 engine. I have flown it for several years without the extension, and now have another year with it installed. I’m sure if I carefully measured the rpm with a tach, or if the aircraft was underpowered in some particular maneuver, I might notice some slight reduction in performance, but as a practical matter, it has made no noticeable difference in performance. Again, the only place to collect oil is the underside of the stabilizer.
In both cases, the extension is made from aluminum tubing available at Home Depot, Lowes, etc. The internal diameter is a little larger than the exhaust opening in the muffler, and I don’t believe the back pressure is increased any substantial amount. I have seen no increase in operating temperature in either case.