They have NOTHING to do with merge collectors. I have used these over the years, and I have dyno tested them too. Dont hold your breath, On a 700 HP engine, they MIGHT pickup 7 to 10 HP. What they do do, is increase the mid range torque, as much as 30 foot pounds(again , on a 700 HP engine) unless you get them almost for free, they are not worth the money.

JOE SHERMAN RACING ENGINES