IMO the VVIS doesn't deserve this much praise. Sure it changes intake volume for a small gain but it's at the cost of a very convoluted / disruptive intake airflow path, especially when compared with any ITB setup.
The VVIS system doesn’t cause a convoluted intake path. The intake air has a pretty much straight shot across from the airbox into the upper chamber of the intake manifold. From there, the air flows up into the intake runners and on into the engine. Above 4800 rpm, holes in the floor of the upper manifold chamber open up, changing the effective volume and therefore the resonant frequencies but the air still flows straight into the upper chamber and from there up into the intake runners. The holes in the floor surely disrupt the air flowing across them somewhat when they are open, but they don’t change the path of the airflow.
FastraxTurbo here on NSX Prime dyno tested the impact of the VVIS on a naturally-aspirated NSX. Across a 1700 rpm band in the midrange the VVIS added up to 11.5 hp and across a 500 rpm band at the top of the rev range it cost up to 3.5 hp. As you said, it seems that Honda’s engineers were trying to build a road-drivable GT, not a racer, and the VVIS helps with that.
If something is really strangling a stock NSX’s engine, it doesn’t seem to be the VVIS system. Getting rid of it only freed up about 3 hp at the redline.
To those commenting that ITB's "only free up air the flow" you're forgetting the the tuned length effect that only comes from a designed trumpet.
I fully agree that resonances are very important. To get the most horsepower out of a naturally-aspirated engine, you have to get the correct airspeed in the intake runners or trumpets at the rpm where you want to maximize power, you need the intake system to resonate at that rpm as well to force even more air into the combustion chambers, you need to make sure the path of the flow is smooth, and that the engine inhales cool air from outside the engine compartment.
As best I can tell, the cross section of the stock intake runners is 1801 mm2, which is equivalent to a 48mm port. The airspeed you get depends on how much air is flowing through there per minute. SoS’s ITBs have a 48 or 50 mm diameter and a throttle plate is in there as well blocking some of the cross section. The airspeed past the throttle spindles is probably similar to the airspeed in the stock runners so that doesn’t look like it’s the key to more horsepower. I’m not sure how the length of the stock runners compares to the ITBs but that will impact the resonant frequencies and therefore the rpm at which torque is boosted. In order to increase the number of frequencies at which the engine gets a torque boost, Honda designed the VVIS system. It does increase the number of rpm at which resonances boost torque but at the cost of a slightly rougher path for the flow when the holes open up. In addition, the air can flow through straight ITBs easier than through the curved OEM intake runners even if they have the same diameter, but I’m not sure how many horsepower the gentle curve of the OEM runners really costs.
With 48 mm ITBs, I’d expect the air to have a slightly less restrictive path but that there would be less rpm at which resonances boost torque. So more horsepower up top but losses at some rpm lower down. I don’t understand the physics of how a pretty much stock 3.0 with ITBs can gain horsepower at all rpm and up to 65 in the midrange - that’s more than you’d get with a CTSC! But if more dyno tests show the same results, the ITBs must work their magic somehow.
