Just installed my new header, but before I did I noticed on where one of the runners met the flange there was a slight lip, So I dremeled the lip away to make it smooth, my problem is this. There was lots of metal swarf left in the header and I forgot to flush it with water before I fitted it. stupid I know, is there anyway this could damage the cat or anything else? thanks.

 

It probably won't ruin the cat, but it might damage one of the o2 sensors. Just unbolt it from the cat again (only 2 bolts) and then turn on the car and rev it to blow the rest of the metal flakes or what ever out.