For a two step header tube, the tuned length starts at the exhaust valve head, correct? So for a 14 inch first step, 3.5 inch from valve head to port opening, then then 10.5 from head to end of first step, right?

The headers are just an extention of the exhaust port. PipeMax factors it in to it's calculations however, so the data it shows are the tube geometry I believe.

Wow. I am surprised on lack of response after 350 views. Guess i am not the only one in the dark on this. But as LA pointed out, pipemax changes its tuned length recomendations to compensate for the distance from valve to header flange. Input zero rather than 3.5,, and 3.5 inchs extra length shows up in the lengths for tuned pipe length. Since my choice of tubing for each step is slightly bigger than recomended, i intend to err on the slightly long end of tuned length. IMHO i think that if i had set my first step length from the valve head using the short end of recommended length, i would be seriously short for the first
step.

That might be technically correct but that isn't how header mfgs measure things. And it might not be technically correct unless your first step matches the exhaust port. Most headers are bigger than the exhaust port so the first step is right at the header flange. Calvin talks about this a lot. It is his #1 pet peeve.

Thanks for the reply Andy. Who is Calvin? I would like to read his posts, or writing. It looks like i may have to open up the flanges to match the heads. I see they hang into the ports in spots on my old 440-1 heads. Don't have my new 572-13 yet, Todd can't get valves to finish them up. I hope i can get this motor assembled and dynoed before fall!