Well Currently I have an outlet diameter of 4 3/4 inches and the plane fly's well and fairly fast but it has ton's of low end thrust for very short take offs for a ducted fan. So I am willing to sacrifice low end thrust for speed.

I spoke to a few guys and they suggested that I could reduce the outlet diameter by 1/4 to 1/2 inches and it would help dramatically in the speed of the plane but the low end thrust would drop.

I am curious to know about the opinion out their on this way to get more speed from a byron setup.

Are their other options available ?

Enjoy!