Window in rear of piston?

Yesterday at work my boss was telling me he had a '95 KDX 200 with a 220 kit in it. It was put together by a local tuner in Ohio. He said it ran great. After riding it awhile the tuner had him tear it back down then he cut a small "window" in the back of the piston skirt, I think he said it was about 1/4" high by 5/8" wide. He said the difference in the  bottom  end was amazing, making it like a four stroke, but still just as fast through the gears. He highly recommended it. Anyone else hear of this or try it? :think: