| the overbore "unshrouds" the valves, and you pick up some power due to the improvement in airflow; probably more from that than from the small increase in displacement. To define valve shrouding, imagine the path of the air that enters the cylinder on the cylinder-side of the valve. It runs into the cylinder wall before being directed back into the cylinder. If the cylinder wall were further away (overbored), there would be more room for air to get through that space, and into the cylinder. I do not know if that is as big an issue on the VG pentroof design; overboring may have little effect on valve shrouding in this motor design for all I know. But that is at least one reason that one may want to overbore in a performance situation. I hope that's right, because it sounds good.
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