Darin Morgan talks about it a lot. Its basically a ratio of flow vs curtain area and valve size. Basically if you have a 2.02" valve that flows 280 cfm and you move up to a 2.05" valve and it flows 281 cfm you will most likely lose power and a bunch of it. So if you move to a 2.05" it better move a proportionally greater amount. So with these heads flowing a whopping 284 with a 2.08" it has a very poor discharge co-efficient. If you search Speedtalk you will see this and the math behind it discussed a lot-and it absolutely works. J.Rob