I tube and redrill the two common wall bolt holes on every head I port. With a 2.08 valve I’m at 334 cfm so far on a set of heads I’m working on for my duster. I could never offer a set like this to customers because of the time involved. The set I’m running now I did in 2008 and max out at 318 with the intake on and would run 9.30 in the 1/4. I’ve changed things a lot since then including my ability to do a good valve job.
