After speaking with Dave today and expressing the complete story, It is concluded that the GP 176 just simply makes too much power with the Smooth Pipes and thus, the CF back plate failed. As many of you already know and I am just coming to the conclusion of....It's been said many times, that CF back plates just can't withstand the output of the larger motors. (Weird how my 157 is doing so well.) Whether it be heat or vibration or just pure grunt, they all seem to fail over time. I was lucky. Mine failed in the most optimal way possible. Thankfully it was caught before a second flight. It could have been catastrophic.
I think that it is stellar that you are digging into this with both feet.
But......................
There has been much discussion when it pertains to the 150cc and up engines pertaining to heat, CF backplates and CF props. Unfortunately, that type of discussion could blow up at a moments notice. Maybe not so here, but the potentiality is there. I've had the same thing happen to me, as you probably seen on that Mejzlik 30x12 prop I sent you to test. Had the prop on my 157 CSTS with a CF spinner and backplate. 4 min into the 1st flight, I heard something unusual. Killed the engine, and landed. Pulled the spinner cone and 6 bolts were loose. Everything was still warm, so I tightened everything up, let it all cool down, and proceeded to go fly again. Again, 4 mins into the flight, same deal. But, the same day, I tried the 31.5x13 Engel, and it was flawless. Made 2 full 10 minute flights. All was good.
I feel that RPM has something to do with it as well. But I made up a little rule of thumb, and I live by it. CF prop/CF backplate = No go. Wood prop/CF Backplate = YAY! Reason I say that is......... I ran a 30x12 Xoar ENP with a full 5" CF spinner, backplate included. Never once did the prop loosen up in 2.5 years.
I'm definitely not saying that you are wrong, but you have a different thought line. And it is intriguing.