Because I don't think there is enough velocity or proper shape in the runners to have much impact. There has to be a venturi effect which usually takes some sort of reduced and expanded nozzle. I guess it's possible though. More likely, there is 2" HG of vacuum in the plenum with little or no restriction in the runner, thereby showing 2"Hg vacuum all along the runner. The only way to tell if there is restriction in the runner is to check the vacuum in the plenum and in the head intake port (very difficult) and see if there is a difference. If there was increased vacuum in the port, say 3"Hg vacuum then there is a 1"Hg restriction in the runners. This would take a lot of doing and I'm not sure what it would gain us. Obviously the better the manifold the better the power since that's the purpose of the test. Even if there was a restriction in the runner but it made more power we would say it's better. It will be interesting to see if the power goes up or down with porting.
JIm
