The standard intake on the VR/VS is enough from stock to provide the engine with all the air it needs. The only thing is, at slower speeds, the engine gets hotter, and there is less airflow around the engine, meaning that the air that goes into the intake will be warmer than ambient temperature. This results in slightly more fuel use to make the same or less outputs of power.
Putting a CAI on just means air is sucked in from a location that is not effected by temp as much. Doesnt do anything for the flow of air, just means slightly lower temp. If you have a stock VR/VS, and have added the CAI on, you can probably vouch that there is no noticeable difference. The power that the manufacture specifies, in this case 147kW, is going to be when the engine is really working. As I said above, the airflow isnt any different.
If they were to compare the amount of fuel used by a VS and a VT, sitting in traffic, they would likely find that the one with the CAI was using slightly (very slightly) less fuel and having a bit more power available. If they were then to both let loose on a freeway, they could probably both pull even power from the engine.
Also remember, that 1kW is 1000 watts. If you know electricity, 1000watts is a fair bit of power.
According to carpoint.com.au (
http://carpoint.com.au/car-review/ce2553.aspx), the extra 5kW the VX can put out is due to:
"A new drivetrain control computer with 33 percent more memory and a new inlet manifold are the key changes. The boost in computer power allows individual cylinder spark control, while the diecast inlet manifold has a centrally located crankcase ventilation outlet. Both measures contribute to the improvements."
The VY was also set at 152kW, so no increase there.
