I don't think the SF can produce 1.8hp at 11,000rpm.

I just finished bench running mine with a Mac's 1062 10cc long stroke quiet pipe. I'm doing the final adjustments before installing the engine in a plane.

Here's what I got with the header cut to 5 3/4"

79° and very humid
Powermaster GMA 5/22
new OS #8
APC 12x8
11,741
1.67hp
9.52lbs. static thrust

My engine would have to turn this prop at 12,000 to make 1.8hp. I guess it's possible with more nitro a bit more trimming of the header. But, right now the needle valve has a broad adjustment range and acceleration is very linear for a pipe (no sudden leap in rpm). In other words, I'm happy with were it is right now. It's operating the way I want it to.

Maybe I'll buy a 12x10 and see what it does. I'd be very surprised if it could hit 11,000. BTW, my pipe is adding about 1,100 rpm over the stock muffler.

David