You don't want the headers to "disperse heat". The more the heat disperses, the less pressurized the exhaust gas in the primaries and collector is, and the slower it travels. Your cast iron manifolds are actually great insulators, and keep a lot of heat out the engine bay and in the manifolds. Stainless steel headers on the other hand are terrible insulators (uncoated). They let a lot of heat in the engine bay, which is bad for several reasons. First off, your intake is gonna be heatsoaked, and sucking that hot air in. Secondly, your IAT sensor is gonna read higher (especially say if you have to idle in the pits at the track more than a few minutes). As your IAT sensor reads higher, it starts pulling spark, and the car runs like garbage.

Lastly, and the biggest reason why coating headers is important is, because an uncoated SS header is like a hose with a million little holes in it. Picture that hose spurting water everywhere out the holes. Your uncoated header is doing the same figureative thing...radiation heat out the header and into the engine bay. If you have a lot of holes in a hose, the end result is that the water travels slower out the end of the hose because it is less pressurized. The same thing happen with a header...as heat is radiated through the stainless steel, it becomes less pressurized, and leaves the car slower. Coating the header is like plugging all those holes. It keeps the heat inside the primaries/collector.. which increases exhaust pressure/velocity leaving the car (since hot air expands). This means the hot exhaust gas leaves the car faster and is not radiated in the engine bay. This pressurized exhaust gas also has a vacum effect, which pulls more air in the cylinder head as it leaves, making your engine breathe better.