[BLUEOVALBOY]

"With less heat and less back pressure we are allowing the air pump (engine) to work more efficiently at higher rates of effort which will free up horse power at the same time."

Clarification on less heat:

You do not want the exhaust running cooler, By replacing with high flow headers or h-pipe with stainless steel or ceramic coatings this will let less heat escape ,keeping the engine compartment cooler. But intern it will keep the heat in the exhaust, which will increase the flow and cut down on scavaging.