Honda used ATAC valve in the early 80's. Its a chamber in the exhaust port of the cilinder.
It changes the volume of the exhaust, it's a bit like chancing your exhaust pipe wile riding.
The exhaust gasses leeks true the HPP or Kips into the space were the valves are.
So the powervalve cover changes the exhaust volume a bit like the old ATAC. Greg Albertijn used it in 99/2000 or so
on his suzuki for more bottom end power. 10 or 12 mm spacer or bigger valve cover.
dutchie