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I guess I'm confused. I took from this that there wasn't a discernable difference between manifolds and headers. What didn't I understand?



At that power level (300hp) there isn't much difference. As power goes up and with more aggressive cam timing, the HP difference between each exhaust type will be larger.

Similar to Hot Rod's 383 intake test a while back. In the mild state of tune there wasn't much more than a 10hp difference between best and worst, but at 450 hp or so, the spread was more like 40hp.