This is old thread...But since it is bump again, i guess i will share my experience. My metallic ultimate HFC. Metallic are usually hold up better than ceramic ones. But it melted down really good! I ran with my SC 350z setup. over 500 dollars pieces fly out in 3 months...lol





Here is some info. But this info is about ceramic ones.
http://car-sound.com/04basics/04failures02.asp

 

here's mine

first pic, the rear side of the piece that flew out the tail pipe -- NOTICE HOW THE VISIBLE PART OF THE CORE LOOKS FINE!

second pic, the center of the core from the same piece as above

third pic, the rest of the core after I removed it from the (now) midpipe