axhaust scavenging is accomplished with full lenght (long tube) TUNED headers.

What causes the scavenging is that the exhaust gases pulsate (or flow in a bubble) down the header. When this "bubble" reaches the collector, a pulse of negative pressure is sent back up the header tube. Tuned means that it reaches the exhaust valve just as it opens, sucking the new bubble of exhaust gas out of the cylinder.

Wrapping your headers is only a means of keeping the heat from the header tubes from heating up everything under the hood. Basically, ceramic coating does the same thing.

Frank