I'm replacing some valves on a 6mt head and was looking at part numbers to find both intake and exhaust valves of auto and 6mt share the same part #. Now someone very reputable has told me that the 6mts have slightly bigger valves on (i think) the intake side. If anyone can shed some lights it's appreciated

 

Nope, theyre the same.

 

Someone very reputable is wrong. They are Same for both auto and manual .

14711-PGE-A00 VALVE, IN.
14721-P8E-A00 VALVE, EX.

 

You are thinking of the difference between the regular 3.2 and the Type-S. Type-S valves are larger on the intake side.