A not so recent article in Hot Rod magazine tested many different manifolds, and I was really surprised that the results were so close. It didn't seem to matter if it was a Holly Street Dominator or a Edelbrock RPM, or a tunnel ram. They were only a few HP difference in power at the end of the day. How can so many different people claim a superior manifold when they all perform the same, give or take a few horsepower?

Marketing.

Its not the actual hp#, but where it makes power, in that situation.

Average power is one measure.

Max power is one measure

Max torque is one measure.

Depends on what you want I guess. I one manifold makes 400hp at 5500 rpm and another makes 400hp at 6500 rpm which do you want? Both are making 400hp.

Refering to the 383 test i suppose? While several of the intakes were very close in performance, some were downright awful in comparison to the others. And if you look at part 2 of the test, you will see that the weiand tunnel ram kicked everyones azz.

I can tell you that a swap from an old Edelbrock single plane (tarantula, I think) to an old Edelbrock dual plane (CH4B) made a HUGE difference in low end torque and accelleration off the corners autocrossing with my son's 67 383/4sp Barracuda.

The Edelbrock RPM is a very nice street manafold.