Why would chrome longtube headers turn blue at the collector??

[juiced_94gt]

Well as you all know last week I raced a cobra, beat it and limped home with a knocking engine, well i went through the valvetrain and set it up again, nothing looked out of order after re tourquing the rockers, then i fire it up and BAM the same knock is there, it sounds like it's on top of the motor on both sides but it's NOT a loose rocker, i did notice that after the run on sunday the collectors are blued...what does that mean? I know it's normal for the primaries to turn blue but The collectors were chrome even after the dyno tune redlines and just sunday it happened... Does that mean it's lean or the cats were plugged or something??

 

[Grn92LX]

Its normal, the chrome coating is junk. BBK's ceramic is junk too.

 

[5spd GT]

To expound better...

It is normal, however it is due to heat. Perhaps the end of the collector is sort of a hot spot with a collection of hot gases. It will discolor, and look like a rainbow pretty soon

BBK's ceramic coating is much better, unless you live in the north, and if you don't keep them kept-up, you can have rust issues.

All my friend's BBK Ceramic coated parts like nearly as good as new, besides maybe being dirty. No discoloration or rubbing off.