reduced stems under the valve
That is the FIRST time I have ever read or heard that valves with undercut stems were a detriment to flow. Or did I read it wrong? If reworking the guide sticking up (shortened guide in port also improves flow. Taper and blend the iron boss helps) it would only seem that narrowing the valve stem would help too. Would this apply to all heads or just the vortex? Wow, some serious change in general thought on this one!! Buddy