If the best you got out of a W5 head was 300 the guy was a hack and I don’t care who that was.
No wonder your **** didn’t run with them.
I posted above how I’d fix the W5.
In fact, I’ll say publicly if I had a fresh set of unmolested castings I could easily get 375 out of a W5 head.
FACT.
And it would burn fuel with a combustion chamber that’s far better than most people think.
I don’t need to assume what you don’t know. You don’t know induction and you’re proving it here.
Edit: 400 CFM if I could weld on them.