it's because the vtec on a K20a3 is more like vtec lite lol. It engages at 2200 rpm as scotty said, and all it does is change the valvetrain from operating on 12 valves to 16. It is for fuel economy, not performance, it isn't like a b-series where it changes cam profiles to a more aggressive performance profile. There really isn't much you can do to make it audible short of swapping out for a K20a2.

Side question, I haven't paid much attention to the shitty A3 motors, do they utilize the variable cam phasing like the other K-series?