That is/was a common deal on super stock engines. Its about velocity. It slows the air speed down, letting the engine go up in rpm, which, will make the car et better if its making more power at higher rpm.
Super Stock engines are very velocity limited. Basicay, its telling you your heads are to fast. Its a crutch, and if you addressed the situation correctly, correct air speed in heads, it would run even faster.
Frank