I installed a four piece exhaust system on the panhead this spring and have put nearly 2k miles on the bike riding mostly back roads and the occasional short ride on the expressway. The exhaust was still looking like new until this past weekend, when I took it for a 200 mile trip with a friend who owns a newer RK. I didn’t have much trouble keeping up with him, at speeds exceeding the limits, for about an hour and a half, but when I got home I noticed that my Y pipe has turned black over it’s entire length. The strange thing is that the other pipes as well as the muffler look just fine. Is this normal for these four piece exhausts?