Quote from six_shooter:
the PCV valve is really quite important to the proper operation and logevity of an engine. A proper system will will crankcase fumes into the engine to be burned off, clearing damaging fumes. These fumes acn deteriorate the gaskets, and leave excess pressure in the crank case, without the PCV system connected.
At higher RPM, the PCV system will, when connected properly create a small vacuum, or at the very least less pressure in the crank case, allowing the pistons to move down the bores easier, helping create more power than without the PCV system connected.