Its every bit about velocity and the inertial fill and expell of the cylinder. Thats the whole idea. For a given rpm band, and increase flow cross-section requires less valve activity for equal cylinder fill. BUT, that may not be advantageous for power, within that rpm band.
the key is in the matching up of the port velocity and piston movement without sacrificing any unneeded/unusable flow potential which can get contaminated or slow the overall process down. no dead areas, all useful/quality flow at correct port velocities.
Flow does not equal power. flow equals power potential, but even that is hazy. Yes, a smaller effective cross-section with a quality flow can definitely outpace a larger crossection with equal flow. atleast within equal rpm range considerations, and depending on the situation, possibly all around. the reason is velocity and the associated inertia is what is filling the cylinder. flow potential by itself is not much help. take the port away and just the intake or exhaust valve act like a venturi, and you will not have much.
pro stock racer is not giving away filltime by decreasing duration because of high inlet flow capability. Its not about the numbers (duration/LSA) its about the optimizing the charge exchange within the rpm range that will provide (in the case of an all out effort set-up) the greatest cylinder filling potential (match-up of cylinder volumetric flow, port flow and velocity, static compression) to provide the most response in the rpm range.
When the match-up is made, the engine's revving and acceleration will be stronger, the power to the ground is higher per unit of time.
Its all relative. the specific numbers (durations, lobe separation angles, etc) are not where the trends lie. For instance the old PS truck motors. 114 LSA would be narrow, yet a 360 SS motor would die with a 114 LSA because the exhaust is way too early. yet the 106 LSA on the truck motor would have died.
But its really more than this, because even this is focusing on the numbers. ITs all comes from the timing events. The durations and LSA come from those numbers. So the subject is not about decreasing the intake duration or widening/narrowing the LSA. Its about where the changes are occuring, are the openings staying the same, but the closing is shortened......... ITs in these numbers that the changes to the motor's flow are occuring. the end effect is seen as a duration or LSA change, but its deeper than that. Its happening at the opening and closing points and the ramp rates.
the argument of the pro-stock scenario is not that the shorter intake timing and earlier exhaust are chosen to get the car down the track (they are), but rather the engine paramters (flow/x-xection/port velocities/displaced cylinder flow) dictate those events. And those can be calculated, then finely honed on the dyno and track. but the trends are basically going to follow what the motor parameters are requiring, and not deviate that much. Basically nothing happens in a motor that is not supposed to. It may not can be readily calculated, but its all there. Its an engineering model.
In actuality, I think we are looking at the same aspect of valve evnts, but from two sides. You are looking at it from the vantage point of what is working, I am looking at from why it is working.
Cross Section Engineering