I've read many magazine articles and such on choosing the right port volume for a particular engine build, but I have never tested the practical application of this theory for myself. I know that the larger the port volume, the slower the velocity at lower RPM, and the better the breathing at higher RPM. Conversely, the smaller the port volume, the better the velocity at lower RPM, and the more restricted the upper RPM breathing becomes. What I would like to inquire is the DEGREE at which throttle response and torque are affected by port volume. Is it a really measurable difference from say a 170cc head to a 210cc head, or is it hardly noticeable in everyday driving? With such variance in plenum sizes for intake manifolds of each make and model, I don't see the significance a few cc's of volume could make to the overall induction system. Perhaps some of you can shed some light on this issue. If it is a significant factor, it may alter my cam/head selection in future street builds.