From WIKI:
Nissan Variable Cam Timing (commonly known as N-VCT, VCT or NVCS) is an automobile variable valve timing technology developed by Nissan. N-VCT was first introduced in 1987 on the VG30DE engine. N-VCT varies the timing of the valves by rotating the cam shaft(s), valve lift and duration are NOT altered. The system is implemented with an electric solenoid which is controlled by the cars ECU. Some Nissan engines only have N-VCT on the inlet cam (such as the RB25DE/DET) while others have it on both the inlet and exhaust cams.
not to be confused with VVL:
Nissan Ecology Oriented Variable Valve Lift and Timing (commonly known as VVL) is an automobile variable valve timing technology developed by Nissan. VVL varies the timing, duration, and lift of valves by using hydraulic pressure switch between two different sets of camshaft lobes. It functions similarly to Honda's VTEC system.
The SR20VE is the most common engine with NEO VVL. There have been two main versions of this engine. The first version made 187hp and 145lb/ft torque. This engine was used by Nissan from 1997 to 2001. It is found in the Nissan Primera, Nissan Bluebird, and the Nissan Wingroad.
The second variant of the SR20VE is found only in the 2001 and up, P12 Nissan Primera. This version of the SR20VE makes 204hp, and 152lb/ft torque. This engine is commonly known as the SR20VE '20V'. Although, in automotive terms, '20V' would normally be interpreted as having twenty valves, this is incorrect. The name '20V' is the name of the trim level of the Nissan Primera that it is found in. It is also a shortened version of the name SR20VE. This engine has 16 valves like the rest of the SR20 engines. This newer '20V' engine, is the only SR20 engine to get a restyled valve cover. It also has an upgraded intake manifold, which has longer runners and a larger 70mm throttle body (earlier SR20VE has 60mm).
Another version of the VVL SR engines, is the 1.6L SR16VE. The engine block for the SR16VE is the same as the SR20VE, it also has the same cylinder bore. The crankshaft has a shorter stroke, which lowers the displacement, but allows the engine to safely rev to higher RPM. Although this engine has 1.6L of displacement, it has more aggressive camshaft specifications. It manages to make 173hp. The camshafts from this engine are considered to be an upgrade for SR20VE owners.
From 1997 to 1998, Nissan produced 500 limited edition
SR16VE N1 engines. These engines made 197hp. (DrG: Not bad for a N/A 1.6 ey??? 
cough cough honda suck) They had further upgraded camshafts, upgraded intake manifold untilising 8 injectors and a larger 70mm throttle body. These engines were found in the limited edition Nissan Pulsar VZ-R N1. They only sold in Japan.
The most powerful VVL engine so far, is the SR20VET. The SR20VET is a turbocharged '20V' SR20VE. It uses a Garrett GT2560R turbo charger, and makes 280ps (276hp). Nissan's technical information about this engine states that it is 9:1 compression ratio, but it really adds up to 8.8:1. Compaired to the SR20DET (used in the Nissan Silvia, and Bluebird), the SR20VET (aside from having VVL technology) has improved airflow in the cylinder head, higher compression, and also improved coolant passages.
One difference from Honda's VTEC system, is that NEO VVL engages the change of intake and exhaust cams independently. On the SR20VE the intake camshaft is switched at 5000rpm, and the exhaust at 6500rpm. However this trait was not included on the newer '20v' version, as both camshafts engage at the same RPM.
