I've got the full volume of a 78 tube between the reg and valve, call it something very close to 50 cc's. Port work, I assume you're referring to the transfer port, the valve exhaust port is stock, the barrel is at .166" IIRC, or about the same as the poly tubing. Don't see how opening it up more will gain me anything. I could take more metal off the front of the valve, but again, I don't see how I'd gain anything, it already has far more free flow than the valve can use. I'm using a tapered spring, .346" OD at the big end down to .251" at the small end, which fits on a spigot turned on the valve head. Pretty soft, wire is only .027" vs. .035" for stock, and 13 vs. 6 coils. My pedestal is really more of a spring guide, just a short Delrin piece that sits in the recess over the hole in the front of the valve extension and keeps the big end of the spring in place.
I will say, I was surprised at the very large difference in velocity I got with differing valve head diameters. The actual seat profile doesn't seem to matter, I've tried flat, conical, and "toilet plunger" style, the only difference was in quality of seal, the plunger style seems to give me the best seal, I've had valve leaks of varying severity with the other styles.
I've had to do some back tracking, I have a terrible habit of making more than one change at a time
. I'd opened up the valve port on one valve to .228" (#1 drill), and used a 3/8" plunger style valve head. Power dropped from 30 to just over 20 fpe. Two changes at once, didn't know where the problem was. So I tore it down again, went with a stock valve port and the big valve head, no change. 5/16" valve head, back up to 30 fpe with either size valve port. This series of tests, more than anything else, is what has me thinking I may be at some kind of limit, and logic tells me that the limit is regulator pressure. But I'm at 1200 psi now, I don't think I want to push a stock QB tube much higher than that. And besides, 30 fpe from that is pretty respectable, don't you think
BTW, don't take anything I've written here as meaning I'm NOT going to try your suggestions, I almost certainly will. I also still have one untouched valve on hand, which I may do some more back tracking with, kind of a reverse base line thing. Later, and thanks.