http://www.wallaceracing.com/header_length.php
A tid bit. Some calculators, formulas and performance recommendations use the tube's INSIDE diameter. If that's the case you would need to subtract twice the tube's wall thickness from the outer diameter.
If so that header material might be 16 gauge (.062") or 18 gauge (.049").
One example here:
https://www.discountmags.com/magazin...is-issue/12912
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__________________
'70 TA / 505 cid / same engine but revised ( previous best 10.63 at 127.05 )
Old information here:
http://www.hotrod.com/articles/0712p...tiac-trans-am/
Sponsor of the world's fastest Pontiac powered Ford Fairmont (engine)
Best time 5.13 at 140 mph (1/8 mile) , true 10.5 tire, stock type suspension
https://www.youtube.com/watch?v=qDoJnIP3HgE