I have. The flow increase was small. I think it was 5 CFM or something.
I didn’t care about the flow. The valve weight was what I cared about. I forget what the weight savings was, but at that point using 5/16 stems was cheaper than Ti valves, which I eventually went to.
Im not sure I can prove it, but any time you put a round section in an air column it makes turbulence and IMO that’s never good, but what we get to live with.
