Setting your CG right is the most important thing in regards to being able to hover and flat spin correctly with a Knife. Mine is set at almost 3/4" rear of the recommended CG. Hovering is a cinch and flat spins are absolutely flat. Plane climbs when put inverted if I don't touch the elevator. BTW, this is using a mere MVVS 40 (w/ tuned pipe) and an APC 11x4 prop (balanced).

In regards to the Rossi pipe for your OS 46? How far away is your tank from your engine? I've got one of these setups and it runs silky smooth through transition. Even more linear than with the stock pipe. Yes it is louder, but I like the sound of a tuned pipe... What I have found is that when using this pipe, tank location is a bit more finicky. You'll want to keep the fuel tank as close to the engine as absolutely possible. I tried my Knife with a TT Pro-46 with the Morris/Rossi pipe and the fuel tank still in the wing and found that it did not produce enough tank pressure when the plane was vertical... I had to set it VERY rich on the ground to do any hovering, and transition (when the plane was not vertical) suffered. Moved the tank closer and the engine ran as well as when I bench tested the engine/pipe combo... BTW, I'm getting 16k rpm on my TT using this pipe (using an APC 11x4 prop). That's 2000 rpm more than a with the baffled stock muffler. It makes a HUGE difference when pulling out of a hover vertically!