Re: "Also sometimes 90 degrees will create muffler interference with the fuselage so it is a good idea to check."< Ya, depending on which fuselage, sometimes the side mounting means that the muffler is too tight up against the plane. I had this on a H9 Cherokee. Solved it by adding one of those muffler extensions. Some planes are designed with that in mind and have a groove in the fuselage to allow clearance for the muffler. On my Stuka, I had tio make my own groove and cover the gap with fiberglass. [8D]