[cammedlx]

If the cat was 100% restricted it would cause noticible running problems..But the honey comb inside can become disloged and cause enough restriction to have it overheat and become cherry red.If it was a vaccum leak or timing issue the headers would glow red before the cats.Also if it was dumping excess fuel into the pipes the mofo would backfire like chitty chitty bang bang once the cats got that hot because there would be no way for that much fuel to enter the pipes without igniting and causing backfires..I would take a rubber mallet and "tap" on the cats and listen for noise..If it sounds like some rocks in a can the honeycomb has come lose.