microsprint9,
A larger exhaust deflector is better for performance on a muffled two or fourstroke engine. A piped engine is a different story. On my twostrokes in use OS91FX, 108FSR, 120AX I only use quiet tuned pipes with exhaust declectors and a piece of aluminium pipe. The dimensions are 8mm innerdiameter x1 thickness x lenght 100mm. It gives a very good tank pressure, instant acceleration from idle and very clean airplanes at the end of the day. I also use OS-F glow plugs in all these twostroke engines.