I'm starting to think I've offended you some how!
Port duration in degrees of crankshaft rotation divided by the time the port is open in seconds, multiplied by the average port area.
Big ports pass a lot of mixture at high RPM, but may make less power at moderate revs. Raising ports to make them open longer will make them larger. Might make the engine become unusable. Ports can be made wider, to give increased flow due to increased area but NOT increase their duration. Increasing the time area - more flow/volume in the same amount of time due to an increase in the port width. A balance of time and area designed to give power and delivery for either normal everyday riding or top end power. That’s where experience tells! I understand but have little experience.
There are equations that I don’t profess on knowing or using! To compare against proven dimensions that are tabulated.
The patterns show that one cylinder has wider, shorter small transfer port. So the timing differs there. But the flow may be the same! The large transfer port on the earlier barrel sleeve is slightly smaller but has same timing/duration (same height position and dimension but 1mm each side narrower) so the flow will differ there. The inlet ports on the earlier barrel has longer duration (higher) with the same width.
I've read tuners widening exhaust port by 10mm raising by 2.5mm. Lowering inlet by 2.5mm, increasing width by 15mm!http://www.ozebook.com/compendium/t5005.htm
I know ideally a matched set of barrels would be best but how much 1 mm in any direction would make I don’t know. Not sure the passages are similar size either.
4 strokes increase flow/mixture/exhaust by the camshaft (cam lobe size and profile give lift of the valve and duration of lift and speed/acceleration of valve opening and shutting) also valve size, profile and seat profile, passageways/ports size. Polishing port bores has very little effect. In fact smoothing them, then adding a few dents/bumps just below the valve heads to disrupt flow increases turbulence when entering the cylinder to improve burn. These valves obviously are in the cylinder head. These bores are port free.
Anyone would think we are talking rocket science here! It's a 2 stroke!
I'm not starting from scratch, only altering ports by 1 mm or 2