hi, the fact remains, if the stock manifold didn't flow good, the MPH would be slow!!!!! from seeing your car run, that 340 stocker will out run your 14to 1 tunnel ram, roller cam car!! back in the early days of S/S racing, the AVS manifold was way faster over after market manifolds of the time!!! finally ,the manifold people built manifolds for the 340/360 that worked better!! valve lift doesn't come into play.
