Sure I do. You just don't accept it. You can go buy the shop, dig through all the dyno runs and learn for yourself.
Better yet, why not spend your own money and dyno your stuff? Then you'd know. Now you just guess.
There is power in headers. Plenty to make it worth it.
Did a 383 for a customer, in a Nova. Begged him to buy 1.875 headers for it. BTDT. All his buddies and the keyboard heroes told him that that would KILL all his bottom end, make the car miserable and I just like spending his money. He was a returning customer, yet he wasn't smart enough to learn.
So he buys the 1.750 headers, and again, his buddies and the interweb world told him they were too big.
When I ordered the cam, I called out for 1.750 headers, rather than the 1.875 headers I wanted. Built the combo around HIS headers. Of course, since I'd done this many times before, we had 1.875 headers there to test.
That day, his buddies showed up, because they are all so smart they figured the big headers would lose power and we'd skew the dyno numbers to "trick" him.
We flogged his engine and made him happy. Then the 1.875 headers went on. And, just like I said, it made more power. Everywhere. IIRC it averaged 20 HP everywhere. Made more power fro the bottom of the pull, all the way up.
And it would have made more, but the cam was ground for smaller headers. We could have used a different grind for the bigger headers and made even more.
That's why you dyno test. It either proves, or disproves what you think you might know. The track can't do that. Way too many variables. That's why all the Pro Stock and Comp guys have a dyno. Because they are dumb. And most good engine shops have a dyno, and use it.
