Don't wrap the exhaust wrap all the way to the flange. The wrap does too good of a job holding heat in the metal. Street rodders are finding their header pipes cracking at the flange from the heat. If the wrap starts like 6-8 inches from the flange then there's no problems. Yes, wrapping to the flange makes HP in race cars but when you'r a racer headers are considered a disposible part, like in NASCAR or NHRA.
Most of us regular people can't afford this