X or H?

I ordered a set of Doug Thorley headers in about 1998 for my 65 Valiant. I didn't know it when I placed the order.....but I was talkin to Doug Thorley hisself. LOL I had a long conversation with him after I fell out from shock. He said that he had done lots of testing through the years on most every kinda crossover you can think of and the only thing he thought they did was make one sound less "crisp". He actually said in some cases, power on the dyno went down. Just food for thought.