The RB25DE and RB25DET engines have the NVCS Nissan Variable Cam System on the inlet cam. This should not be confused with VTEC-type cam timing, as NVCS only adjusts the rotation of the cam and does not alter the lift or duration of the valves. NVCS engines can be identified from non NVCS RB engines by the cam gear cover (the NVCS RB has a bulge on the cam gear cover) at the end of the inlet cam.
Nissan Valve-Timing Control System is mainly for low and medium speed torque production because the vast majority of the time, engine RPMs will not be at extremely high speeds. The NVCS system can produce both a smooth idle, and high amounts of low and medium speed torque. Although it can help a little at the top-end also, but the main focus of the system is low and medium range torque for more power and torque at lower rpm.
Also try this link, has a graphic on differences with and without NVCS.
http://nissanskyline.6te.net/NVCS.htm :sorcerer:
Sik sig BTW.