I think you would blow lots of plugs before you toasted an engine. It doesn't take much metal swirling around in there to blow the plug.

And out of all my pipe running days, I have to agree with Dave that if you butt a pipe up to the header enough for it to rub, it'll rub enough off to make a gap right quick and quit rubbing. I always put a length of aluminum tubing inside the silicone coupler to keep from having a long piece of unsupported silicone tubing...the silicone burns out quicker and also pulses if left open to the exhaust.

I've pulled those pieces of aluminum tubing out to make a cut and you could see where it had rubbed the pipe/header. I had lots of hours on lots of engines, if the rubbing was causing my engines to blow, or my radio to glitch, I'd have known it.

Just my observations. I did recently have a spat of glitches on a piped engine powered plane, but that header was run up inside the pipe...I don't know if that's what caused the glitches, but when it goes back up it'll be (almost) butted up, not slid into.

Another thing...There are pipes that connect directly to the engine with just a silicone O Ring sealing the exhaust. There is no way to keep the pipe from rubbing metal-to-metal on the engine. If this caused radio glitches, looks like these engines would be unusable in RC planes.