exactly oc.... sorry if I'm not really making any sense. The whole purpose of exhaust tuning is to find the right diameter pipe that will facilitate exhaust speed (as you just described) while adding as little backpressure as possible(like a perfectly straight straw). Inevitably, you need to have a little backpressure in order to get that speed, but the goal is balance it just right so that pressure is minimized and speed is increased.