My afternoon was fruitful yesterday, although I got zero prop data.

What I did learn is that a tuned pipe "reacts" very strongly to being 3/8" shorter on the baffle distance!

RPM figures were waaaaayyy down and the needles were not happy. I thought it was caused by my static line modification, so I took the line off and it made no difference. Thought maybe the H needle was perhaps moving around on its own. Nope. Only later did I notice that my Velcro pipe strap had slipped off the back of the silicone insulator on the back of the pipe, then I put 2 and 2 together and realized the coupler distance was incorrect. Gotta re-do that to the magic number: 27-1/4" plug to baffle.

Good news is, the coupler held tight and didn't leak one molecule, and the header held firm and was not bumping anything in the forward pipe tunnel. Ran very quietly, but then the RPM with the 18.1x12 was ony 6300 because of the pipe issue.