| be from each other, even when totally stock. There are specifications in the service manual that have tolerances, +/- this or that, and then there are anomalies in the casting process that aren't even discussed in the service manual. I've seen enough heads to know that they are not all the same, and namely in the most important areas when it comes to flow - the valveseat-head interface being the most variable from one head to the next. Performing the test with a head attached, and knowing that this area of variation from one head to another is going to have a significant impact on flow of the test setup (head+manifold), the manifold is going to play a significantly smaller role in the flow results and will skew your data. The only thing I am certain of in the data Nixit provided is this: Anything is better than stock.
Mike Smith manifolds with a head having larger valves outflows them all with stock valves. Anyone with any general sense could have told you that information. Other than that, most of the results are all too close to each other given that you could easily have a 10+CFM difference between two stock heads, and then add to that the adjustment of valve lift and its effects, and all that data just goes out the window. Your presumption that all stock heads are identical is where you just went into the deep end.
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