Originally Posted by MattRS1600i
I thought larger ports/valves would lose torque across the rev range and that torque had some kind of relationship with the speed of airflow more than the amount
The old thin pipe/thick pipe analagy?
you are half right, but for the wrong reasons.
having larger ports and valves drops gas speed, dropping gas speed at low rpm can result in the cylinders not filling as well, so the amount consumed in a cycle drops, and its this drop that then results in less toque.
conversely at higher rpm opening things up to allow the engine to breathe more easily actually results in an increase in torque, as it improves the amount consumed not reduces it.
effectively every point in the rev range has a different optiumum port size, valve size, cam duration etc, go either side of that size and you get less torque (and hence less power at that point in the rev range)