[900HP]

Originally Posted by 77 TRASHCAN

I've got the PHR magazine, the last one...I guess ever...and have read the thread.

The end of the collector looks like about 2-2.5" dia...LOL

I've seen Tri-Y headers on a successful pontiac stock elim. car recently, close to what you guys made, but they appeared to go more for the equal length effect...
Thanks for the attitude adjustment on what size primaries, HAVE to be...LOL

My good friend, and other racing 71-72 GTO stockers (in the early 80's)(specifically 455 HO's) found out that when they decreased the primary tube sizes, the cars went faster...Hmmm.
Thanks again

Headers are 1 3/4" step to 1 7/8" primary tube with 2 1/8" secondary tube. The collector choke is 2 1/2" tapering out to 3". All lengths were within an inch of target. Not shown in the photos are the 3" collector extensions we used, I *think* they were 11" long..... Not mentioned in the article was the 8" of crankcase vacuum we could pull with the pan-evac setup