So the learning point is headers may give large improvement depending on the combination, but also just a marginal improvement with different combo.
You could substitute the word “headers” with a variety of other components and that would still hold true.
You have to look at tests like this through the lens of “how does this compare to what I’m doing with my own package?”
On a 250hp 7.7:1 400-2bbl the difference between headers and manifolds will be pretty minimal.
On a 1000hp 572 with B1 heads it’s probably going to cost 150-200hp by putting manifolds on it......... maybe more.
The results of any test like that only shows you one thing......... how that exact particular combo responded to those exact particular changes.
Which is just as likely as not, going to have any relevance to what you’re doing with your own car.
