Standard exhaust manifolds
 

Are the standard low hp GTO exhaust manifolds interchangeable throughout the years? 4bbl vs tripower or 67 4bbl on up. Are their outlets different diameter? Not worried about casting numbers.

The short answer is yes. There were different configurations that were on some years of big cars and F-body. But the basic rear dump log manifolds are functionally the same across years and engine sizes. The manifolds on a tri-power GTO are exactly the same as the ones on the same year 326. They could also be swapped on to a 350 or 400 or 455 in an A-body up through the late '70s.

My confusion was I saw on the Wallace Racing the same casting number manifolds used on motors that were supposed to have 2"headpipes while others had 2 1/4". Were the 2 1/4" necked down to fit. This info has departed my brain thru the years and you just can't go out and order them anymore.

The standard log manifolds will accomodate both pipe sizes.

also please don't forget that there are some two stud, and three stud manifolds;
I believe that somewhere around 1973/4 they revised them to have three studs on each side...
(please correct me if I'm wrong!!)

Also, I believe it was the full sized cars that had one of the manifolds which had a center dump - all of the manifolds I have had were F-body or A-body style manifolds.