Test: Couple of pictures of Edelbrock 2831 version of those two intakes. The stock manifold flowed ~343 cfm, and I attempted to show just how much a small amount of change in the size of the port makes in airflow. The ports are still smaller than the scribe mark the owner wanted me to open the manifold up to. The heads are D-3, and they flow 415 cfm with 2.135" intake valve. I have ported several sets of heads for him over the last 30 years. Joe-JDC