Lawrence Conley said there was. Others disagreed. He was the quickest guy around for a long time.
The idea was to stabilize the air and reduce turbulence so that the air would make a smoother turn into the heads which should help in equalizing air cylinder by cylinder.
More recently, the Hemco was reborn with guys claiming it would do the trick better. Remember that I gave one to ttipe to play with as he was following the lead of Red, and, I think, the zddp+ guy....have not heard any results in quite awhile.