Re: Coat or wrap downpipe - any difference?
I don't really have a solid opinion on either. Seems like both have drawbacks and there isn't a clear cut winner.
I own coated headers & they always seem to flake, at least on the outside. Haven't really looked at the inside. And they're not even on a turbo application, so they probably don't see nearly the intensity of heat. Maybe its just cheap coatings, I don't know.
Header wrap definitely has drawbacks too. It does cause the header tubing to see higher temperatures (like was said above) which isn't good (read the disclaimer any of the wrap manufacturers has on their product). Only experience I have with wrap was on Formula SAE race cars, and they never saw real street duty, and usually only had a couple dozen hours on them by the time they were replaced by the next years car.
One area of intrigue is the fact that many light airplane engine installations use wrap. If it was really a serious fatigue problem, I'd think they'd be real concerned about it. And if it was a serious fire concern, I'd bet they'd have a better solution.
Which leads me to the next item: Sealer.
I've also seen several "sealing" products available for header wrap. Some products carried by Summit and such look just like paint to change the color. The airplane stuff (which may or may not be any different) is supposed to be a sealer, which keeps stuff like oil from soaking into the wrap. Aircraft Spruce & Specialty is where I've seen it. Which means it should pose a smaller fire hazard than a coated header, because the oil can't get into intimate contact with the hot steel & flash off.
Just some thoughts to throw out at you.
'Dreamin'
