I had a set of those D3 heads on my flow bench recently with a 2.135"intake valve and 1.560" exhaust valve. 410/300cfm @.800" no exhaust pipe extension. Best set of SBF heads I have ever flowed on my bench in over 20 years. I have had several in the 380-390cfm range, but these shined with a smaller valve. I have been told by many that my bench is consertative, and these heads just flat flowed. I am very impressed with what I see in those heads. Now if they would just make an intake manifold with thermostat housing for a street engine. Joe-JDC