ORIGINAL: Hobbsy
Early on in his racing career Ed Eskendarian discovered that you could take advantage of the overlap between the exhaust stroke and the intake stroke by tuning the intake track and the exhaust header. Using the momentum of the exhaust ''slug'' to create a partial vacuum behind it and having both valves open simultaneously you could trick the intake to start flowing sooner, then by keeping the intake vavle open for the early part of the compression stroke you could use the intake ''slugs'' momentum to keep air and fuel flowing after the piston started upward on the compression stroke. That's why when you look at where one our engines intake valve closes the crank is at about the 7:00 or even close to the 8:00 position.
ED excercised a little imagination and called it the Isky five cycle cam.
Was it really Iskenderian that developed this concept? Regardless. This has no meaning in model engines as neither intake, nor exhaust is tuned. The power improvement due to increased duration is there, but it's because the valves are simply more open when needed.