On my D16Y8, with the resonator removed, you can hear a distinct change in the tone of the intake at about 4800 rpm, but with the resonator in place, you can't really tell a difference. Also, I don't know if any of you have tried this, but if you unplug that vtec solenoid thing and dyno it, you'll see that the dyno graph looks virtually identical until just before 5k; now the torque peak occurs at 4700, and it just drops off after that (be warned, your CEL will come on if you do this though).