VTC Gear?

[Shocker240sx]

Hi, so I just got a S14 SR20 notch top (Black cover with the notch at the end) with the VTC gear. As of now I really know nothing about it, could I get some info on the notch top motor and the VTC gear. I previously only thought that there was just a blacktop SR20 and a red top SR20 on a S13 and a S14.

As much info on the notch top SR and the VTC gear would be very helpful.

Thanks