Running up the engine on the ground, the pipe kept slipping off the header. The pipe is just coupled to the header with silicone and strips, and crammed into the pipe tunnel,. A very quiet setup but the same reason was also it’s undoing – it has no physical restraint from keeping it sliding back so when the 1.60 did it’s thing at full bore the pipe simply slipped off the header.
A friend suggested I rough up the surface of the pipe and header so that the oily silicone wouldn’t slip off. That worked and it ran great for two flights. I did have a cowl problem later on, the screws loosened and I need to drill new holes before it can fly again.
Thankfully it is a simple job to remove the entire pipe assembly, just screw the header off and pull the entire thing out.