If you agree that the exhaust port is a limiting factor-
then why would you think that putting in a larger valve would improve flow???
-Well, since I have some 38.5 valves collecting dust and need new valve seats anyway ;) But next to that: I don't know HOW to improve the port, so sticking with the valve only would be relatively safe. It would improve flow simply because the 'opening area' is larger.

I don't know how many times or how many ways this needs to be said, but unless certain parts of the port/bowl/seat (and at some point even the combustion chamber) are modified, just putting in a larger valve will not improve flow.
-Then please tell me what 'certain parts'.

A lot of this stuff is not that hard to find out yourself with a little testing.
-For porting this is true, a head to practise on is the only thing needed (next to a flow bench) but not for valve sizes, since one would have to machine the seat areas for different valve sizes.


Even if the port itself is limitting, I figured exhaust flow as a whole might become less limitted with the use of a larger valve and seat even when only just blended in with the port and no real port shape changes.
Imo, an exhaust (or intake) system is not like "a chain is only as strong as its weakest link": how could a DGV with 26 and 27mm chokes otherwise out-perfrom a single 42mm stromberg, which is functionally a larger opening then the 26 and 27mm added together? Ofcourse its more complicated then that, and I might be completely wrong in my assumptions, but please tell me. I'm just a dummy still...

btw. did anyone safe this pic:
http://www3.telus.net/public/iadr/V/porting%20pics/b20portingpic.jpg

cheers, ben
--
P131, '65, B20B+M47. P131, '69, B20E+AW71L+LSD. (www.tinustechniek.tk)