[oldman]

I view the exhaust system as a heat sink.

Race engine open header, yep the more heat retained before ejection to the atm, the more HP is to be found, in general of course.

For a street car, especially one with headers hooked up to the factory cat back, to my mind the question is moot, does a coated header which has more retained heat and energy at the header exit point into a muffled exhaust system yield more engine power? I HIGHLY doubt it.

Will my engine compartment be slightly hotter when I'm in grid lock with non-coated headers? Yep.. don't get into a 1/4 mile throw down in the center of Austin at 7:30 in the morning.