The distance between the header and the pipe - handled with silicone tubing - can be very useful for fine tuning the tuned pipe length. I've never had a problem with a 2" 'gap' that exists after fine tuning with each end secured with nylon cable ties. After all, the header is secured to the engine and the pipe is secured to the airframe, right? With this sort of arrangement I don't see how a 'blow out' can occur, unless you have a very short overlap of the silicone tubing on either end.