One casting, Edelbrock varied chamber size the same way Pontiac did. They changed the chamber roof height, then used different length valves to maintain valve geometry and valve gear interchangeability.
(It is my understanding the tighter radii of the curving transition (the "short side radius") between the port floors and the valve seats on the 87cc head is why it flows less then the 72cc head)
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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
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