ORIGINAL: bob27s
a little less prop to start with.
You want the engine up closer to 15,500 for the muffler to really be killer.
Start small, and as you get time on the engine/muffler... then go up in prop.
I went and picked up a 9x7 and 10x5 APC props the other day and had a chance to run the 9x7 today. Peak rpm was about 16,400rpm. Tached it two or three other times at right around 15,900-16,200. I'm gonna need some thrust for pushing a 5lb airboat around, so I'm gonna test the 10x5 when I get time.
Whats the lowest RPM I should be at to still have it using the pipe well?